A fairly simplistic way to think of it is that a lighter bullet will generally be faster and flatter shooting over a specific distance, while the heavier bullet will be slower, but may have greater kinetic or "knock-down" energy.
Looking at various load data, you'll see that the faster hollow points are usually lighter in weight, and will usually be designed to expand more quickly, dumping their energy into the target without going all the way thru.
The heavier solid lead slug will penetrate more deeply (better for some game), but runs the risk of penetrating all the way thru.
In actuality, there are many variables in this. That makes the study of ballitics really interesting!
I didn't think folks still played GURPS. I remember it coming out in my gaming days - the early eighties!
