For my motorcycles I use .032 structural bits, sprocket bolts / brakes, triple-clamp screws and items like the oil drain plug. On cars, bolt-on oil pickups.
I do use .020, like when a tab-type points condenser (Lucas) is inside a distributor, the Cortina GT air cleaner with the nuts and washers inside (eventually they will make rattle noises a cylinder otherwise), or small screws holding some widget inside the oil zone.
Quite a few little items if it's a Baja racer but otherwise that's about it for safety wire.