Painting with a very broad brush (so no one get dere panties in a wad), once you hit the heavier classes in equipped, there is an advantage in being big, even fat. That's because (without getting too sciencey) the larger surface area and mass produces a foundation for greater force. This is compounded by the use of a compression suit. Without the suit, any extra fat is still helpful but not as much as having it all wrapped in a rubber band.
With the lighter weight classes, unequipped (raw), any extra fat is dead weight. You might even get bumped up into a heavier weight class while having no more muscle than a guy 10-20kg lighter than you.
While this is not a hard and fast situation, generally you want to be leaner when lifting raw. If you pack on 10kg of bodyweight to put you in the next weight class, you better have 10kg of new muscle, not fat and water.
If you look at the IPF and CAPO raw lifters, you will see that they tend to be more "powerbuilder" looking than the equipped fatties.
Dan Green. Richard Hawthorn,
Nghiep Luu,
Michael Tucshcherer. Big and small, they are all pretty lean. Not bodybuilder lean, but good enough to walk around with their shirt off.
Once the raw lifters get over 120kg, you do tend to find them a bit chubbier, mostly because having a bodyweight over 120kg (especially drug free) is kinda difficult without the help of some love handles.