Yes, God forbid you need native (low threshold) devices... want to minimize NWell spacing for stacked devices while preventing ESD latch-up... care about capacitance density or voltage variation.

Basically, if you are designing mixed-signal/analog then your PDK (Process Development Kit) either comes from a tier1 foundry (TSMC/UMC), the process is a very good copy (SMIC/GF), or you need a year of support and a one or more full time process support engineers.