I have a design related question. Consider the total assembly of a piece of industrial equipment which is composed of various sheet metal parts and welded frames, what is considered the current best practice approach to mitigate assembly stackup issues?

Is it worth doing extensive tolerance stackup calculations and making sure all the parts are fabricated to very close tolerances. Or is it more efficient to simply allow for adjustability in the design itself, through extensive use of slots and adjustable elements like studs and shims to facilitate design for assembly? See attachments for clarification.