I'm looking at this from two sides.
Would I run CAT5, or even CAT3 just for voice circuits? No. It's overkill, and I can see the point about making off dozens of pairs soon becoming tiring. When I think back to terminating 100-pair or more cables on the MDF of a telephone exchange, it would certainly have made the task very much harder and longer if every pair in the cable was twisted up like CAT5.
Would I use a pair in CAT5 for voice if that cable was already in use or to be installed for data? Quite probably. If you have 4-pairs with only two in use running to the right location, why not make use of the spare pairs?
I think it comes down to a matter of balance.
