I did weld professionally for many years and always had heavy welding equipment to use but I still would have felt lost without my little 110 Lincoln! I did a lot of work outside and some jobs, one in particular that came up often, would have meant trying to string out many feet of heavy welding cable (sometimes nearly 150'). This job site had 120 volts available to power the lighting and some small cooling fans so I would just grab my little Lincoln with it's small gas bottle attached, climb on up there and have at it!
The duty cycle was the only limiting thing here as we were welding machine guards and handrails so the metal was rarely over 1/8" thick but occasionally it would be as much as 3/8" which with a bit of preheating from a torch was no problem either. Those little Lincolns will weld about anything you are likely to tackle with proper procedure and preheating the base metal BUT it starts to get impractical even if it is possible if the job normally would take more than just a very few minutes using a bigger welder. It's up to the operator, if you have all day to do a normally small job and are willing to take the time and extra attention such as preheat and multi-pass welding then these small machines can do some things a lot of people think they can't do but as I said it starts to get impractical and can be a genuine PITA. NEVER buy a 110 machine thinking that these little tricks will make it work anywhere near as good as a larger machine and if the purpose will require welding more than just thin sheet metal for more than just VERY small jobs then you will need a bigger welder. The 110 MIGs can work just fine for body work and other thin metal projects and they can be used for heavier jobs in a pinch but the extra time and prep just makes them impractical for more than that, for instance you may be able to weld a shock mount bracket with proper prep and procedure but it would take a heck of a lot longer to do it and welding a frame just should not be undertaken with one of the little outfits.