do you really need to paint the backs of skirting boards?

Hi all

I've been a carpenter for a good number of years and for as long as I can remember when I've fitted door frames, skirting boards, and architraves I've always knotted, primed and undercoated all four sides before fitting.

However recently I've done a few refurbs where we've removed door frames, skirting and architraves that's been in for a few decades and the backs and bottoms have not even been primed and there's been no probs with it.

So I'm now questioning whether I've being going over the top when others seem to not bother.

I can't see that painting the back of skirting stops it from warping as it is securley fixed in place with screws. Maybe the bottoms of these items need painting as they can get wet from people mopping floors. I've heard the arguments that if a plumbing pipe or a rad leaks the back of your timber is protected but what is the chance of that happening?

I've always thought that knotting the back is a good idea to prevent resin leaking under the skirting board.

Please advise/remind me and others what the reason(s) are for knotting, priming and undercoating the backs and bottoms of trim and door frames......... or is it really necessary at all?

kind regards, Andrew