It depends on the repair. I just finished fixing the area around my headlights on the BMW. It required several small pieces butt welded and then ground smooth to make the panel. On the MGB floor pan repairs, I overlapped and seem welded both edges. It made the car stiffer than when it had a crude showroom stock style bolt in cage. In general small home made pieces get butt welded, and large replacement panels get an overlap, drill, and spot weld. Some panels just get extra metal laid over the existing metal for reinforcement. The rear control arm mounting points on a TR8 is a perfect example of a place that just gets extra metal.