He has had his critics at Turf Moor, largely I think because he lacks height, rarely hangs up a cross to the back post, and because of a penchant, less obvious this season, for lapses in concentration. It is these weaknesses plus a lack of burning speed or athleticism which have prevented him from becoming a regular performer at the top of the Premier League. Nevertheless, those attributes which he does offer make him one of the best plying his trade at this level.
The competitiveness of the central midfield battleground in the modern game has forced managers to do one of two things: require their wingers to tuck in and create a narrow midfield quartet, or withdraw a striker to bolster that central midfield region and ask those wingers to play further forwards and further in field in order to support a lone front man. At the top of the Premiership, Arsenal opt for the former, whilst Liverpool, Chelsea and - to a certain extent - Manchester United take the latter.
Either way, the result is that it now falls upon the full backs to not only defend, but to provide genuine width to a team in attack. Full backs have become football's equivalent of wingers in Rugby: outside backs, primed to come onto the ball with pace and depth to add pace and penetration to the attack once the hard yards have been won in midfield.
As a result the qualities which were once priced in a top class central midfielder - athleticism, pace, strength and stamina - are now precisely the ones which are essential in a top-class full back. Ironically, the orthodox central midfield duo are now generally more reserved, subtle performers. Midfielders who exhibit those more rumbustious characteristics, such as Steven Gerrard and Frank Lampard, are accommodated in more advanced, less responsible roles within a central trio.
Such athletes as are capable of fulfilling the modern full back position are exceptional and rare beings. Yet the best will also be efficient in possession, since they are likely spend more time on the ball than anyone else in the team except their colleague on the opposite flank. And still more significantly, they must be sound defenders, capable of dealing with the exposure which inevitably results from the lack of a wide player directly ahead to share in defensive duties.
And so if they must fundamentally be quick enough to be in the right place to either attack or defend as required, then they must be at least competent in both disciplines. All of which means that the oft-made remark, "it's a lot of money for a full back" belongs to a bygone era in which professional football teams, rather like Sunday League teams, could get away with simply plugging the position with their weakest performer. It is debatable whether there is anywhere to 'hide' a lesser player in the professional game these days, but if there is it certainly isn't at either left back or right back.
Jon Harley can't be expected to fulfil all those criteria for a top-class modern full back, because if he did, he wouldn't be plying his trade at Turf Moor now, let alone next season. But he is quick enough to get up and down the line and to keep pace with the majority of Championship wingers. Defensively, he is tenacious (if not, perhaps, accomplished) in the tackle and capable of covering across his centre halves.
His use of the ball is neat, swift and almost invariably precise whenever it comes under his care. He likes to get forward and when he does, he has the skill to get beyond his man and to link with, and create chances for, others - even without producing a string of crosses from the by-line. Fundamentally, he has sufficient pace and stamina and is competent in both halves of the pitch - and that perhaps modest-sounding endorsement is enough to make him an enormously valuable commodity.
This is especially so at Burnley, where the absence of the resources to attract the superior class of player to dominate a midfield or to provide sheer brilliance places an increased emphasis on close-knit teamwork. It is, if you like, the Arsene Wenger model: if you can't out-muscle them, then ensure you are more skilful, more mobile, and can get more men around the ball to pressurise teams into yielding possession.
Full backs that can double up as both attackers and defenders are essential to that philosophy, releasing two more players to support their colleagues in those central battlegrounds. That contracts the space between players; allowing the team to remain compact in defence to crowd out individual flair. And it also facilitates short, sharp interpassing of the type Owen Coyle preaches.
It therefore follows that, if Coyle wants to encourage that brand of football, he will have to re-evaluate his stated desire to play with two out and out wingers and instead allow his wide players licence to roam, find space and support their teammates inside in the manner of those of Manchester United, Arsenal and at our level, West Brom. And as a result, integral to his strategy must be ensuring that he has full backs on either side that can move forwards to add the width he craves.
Quite simply, it will cost more to replace Jon Harley with a better version than we can afford. For confirmation that this is true, one need only look at the travails of Steve Cotterill these past two summers when he has searched for a right back, a position for which there are far more candidates than for the left-footed equivalent.
That, by the way, is a search which should also continue, because whilst Michael Duff and Graham Alexander are sound options neither have the qualities described above and so by the same logic, neither are the real answer for Owen Coyle if he is seeking to make his team and his philosophy a real success. To win promotion, Burnley must excel in the departments which wealthier rivals neglect and, at the same time, we must find ways to combat the wealth which those clubs can lavish in the departments in which key matches are won and lost.
But first things first. Jon Harley is the first available piece in that jigsaw. There will be many others required in the summer. And, quite aside from anything else, it would be crazy to increase that summer workload by risking the possibility that someone who is arguably our player of the season could walk away from Turf Moor on a free transfer.