Their are negatives too.
Higher center of gravity making it a little easier for you to be taken down.
If you're feet are large it is much easier to sink a heel hook, and toe holds are more prone to injure the knee. You will be almost immune to achilles locks though, unless you're opponent is a master at positioning.
You're legs will be a pain for your opponents to pass, but once they do pass it will be more difficult for you to replace guard than it would be for a short legged person.
You can trap people in triangles very quickly, but long legs may keep you from locking it in as tight as someone with shorter legs.
For every positive your long range your body provides, their will be a negative. That is the yin and yang of bjj that you will have to deal with, and it is the element that allows any body type to beat any other body type.
I've got really long limbs, and I wouldn't trade them for anything.:icon_chee