Low profile cards

whats the advantage to a low profile card and onn that isn't

As ct said, they are meant to fit into low profile cases. Also, it is often an effort to cut costs since it ends up on a smaller cheaper PCB. For a card more complex than a 9400GT or Radeon 4550 having that GPU on a low profile card means the PCB is less crowded and often that the GPU is less effectively cooled. 9600GT low profile cards have pretty packed PCBs and run a little hotter than normal profile cards that enjoy a bigger heatsink and more spaced out components.