seam welding is commonplace for all rally cars and circuit race cars. It is done to increase the rigidity of the body to provide a stronger, more stable platform for the suspension in circuit cars, and to withstand the buffetting dished out by rallying. Cornering forces on the track (and jumps and bumps in rallies) will deliver higher torsional forces through the body than any motor you can squish into your Datto.

My coupe (not seam welded or caged) for instance has stress marks around the strut towers, A pillars and C pillars. Floorpan also separated from the chassis on the drivers side. This is defeinitelty due to cornering forces rather than engine torque!