It's always best to have a certified electrician wire your circuits and I'm not a certified electrician. But as I understand it, your local Power and Light (or REMC around here) usually sets a 220V transformer for your service and runs power to your meter. The voltage coming into your Breaker panel is 240V. All a 220V circuit is is two legs of 110V and a common (ground). In contrast, a 110V circuit has one leg at 110V and a common. All you have to do to run a 220V circuit is to plug a 20 or 30 amp breaker into the panel strip and (using 10/2 or 10/3 cable) run the wire to an appropriate recepticle for your plug. If you'll notice in your breaker panel, a 220V circuit uses up (2) locations in the panel where 110V circuit uses only (1). The size panel determines the number of locations available for individual circuits. My house has a 100 amp service panel, but most newer homes have 200 amp panel for more available circuits.
For my purpose, I wanted a 100V welder so I could take it with me to do light duty welds. For example, right now my MoM has a damned old swing set she wants to hang a porch swing on. It's wobbly as heck, but she wants to use it. It's just a heck of a lot easier for me to take the welder, run a (good sized) electrical cord out to the swing set, and weld the joints. She, nor do most people for that matter, have a 220V outside plug. I can still do other welding project with this Weldpak 100, it just will be much slower.
Everyone should just buy what will work for what they want to do. Just like building your XJ ... build it to suit the type of wheelin" you want to do.
Les