Both ways for each situation...."builders request"
Biscuits with arrow 1/8 flat staples....
Detailed moldings... sides then top....biscuits usually only with plinths
The cased openings I build both ways...
I can eyeball an adjust miter on the doorway to look just as good as biscuit joints....
Seems to me it takes just as long if not longer...biscuit,glue,clamp...three more steps when builders don't ask....
But with 1x4 casing yeah biscuits glue for the win....
"Old school" use biscuits 100% of the time..
Just why are the biscuits needed?
for detailed moulding for 15-20 doors one guy nail one guy cuts is the way