When TIG is the right process
TIG is common on thin-wall stainless and aluminum, on sanitary and food-contact assemblies, on visible architectural work, and on parts where heat input has to be tightly controlled. Because filler is added independently of the arc, an experienced TIG welder has a lot of control over penetration and bead profile.
Cost expectations
Expect TIG work to carry more labor hours per joint than MIG. On a short run that is often irrelevant; on a repeating production part it can dominate the piece price. If you are quoting a recurring assembly, ask shops whether a mixed approach — MIG on structural joints, TIG on visible or sanitary joints — is realistic.