All sorts of things to do with steel pipe - pressure welding isn't going to use MIG (unless the approvals have changed it's stick), airframe isn't going to (that's pretty much all TIG), etc. Welding up some pipe for a hoop stand? Sure! Pipe as a trailer frame? Perfect!
Like I said: It depends on the job. If radiography is involved at any level MIG is not likely to be chosen. If the process is variable it's not likely to be chosen. If the job involves joining the same metals in the same thicknesses over and over again it's your man.
NOTE: These observations are from past experience, and things may have changed.