Very very few, but I've not played many spellcaster heavy groups where this matters more also. The main LR reason for most of my groups is out of healing - which is never really a thing because money is everywhere and potions exist.
There a few fights in the game which require a long rest afterwards. The only ones are where you burn everyone's spellbook down, and that only really applies to Gale and Shadowheart, Wyll - LZ and Astarion like using up all your SRs and need very few LRs. So parties that don't have SH and Gale, or a player character who casts, will not LR much if they play like I do.
I probably LR 2-3 times before underdark and grymforge, and 2 times there.
