Any sense in having different thincknesses of insulation in one room?

Folks,
Recently erected a Timberframe house that had 100mm PU insulation pre-fitted between studs (140mm) in external walls. 1st fix trades are now complete. I was considering fitting an additional 25mm PU between the studs in external walls where no cables/plumbing pipes are ran but am not sure as to the value of this, i.e. is there any return on having say 80% of the room fitted with 125mm deep insulation & the remaining 20% with 100mm? Know now I should have fitted the extra 25mm first & counterbattended for services but too late now I guess. Appreciate any feedback/comments on the alternative proposed. Thanks in advance, apple1

you be better off spending the extra on air tightness tapes and sealing around opes ducts etc...

Thanks syd. My problem from an airtightness point of view (as well as a vapour control layer perspective) is that I know I'll need to 'puncture' the membrane in various places when I come to 2nd fix. For various reasons, I have had to leave some cables loose between the studs & will have to fit dry lining boxes when slabbed. This will mean penetrating the VCl however. How big an issue is this in reality? Thanks, apple1