I'm glad SolBadass and Ladon covered this, EVEN THOUGH I SAID THE SAME EXACT THING IN AN EARLIER POST. orz
Like they said, characters have specific jumping arcs and how they fall during a jump. Character weight specifically refers to how fast a character falls while they are in hit stun. Everyone in BB falls at the same rate while they are getting comboed. In Guilty Gear, this is very different. Here's an example.
A standard combo for Sol is ending a combo with 2D into 236K (Bandit Revolver). Let's compare Ky and Robo-Ky, which have the same hit boxes or very, very similar ones when they are getting hit. On Ky, 2D into 236K will work because he has the default weight of 1.00. On Robo-Ky, 2D into 236K will NOT work (most of the time) because he has a weight of 0.95, meaning he falls faster to the ground than normal.
Make sense?