chemical composition for SDS-PAGE buffer and gel?

[trypsin]

I have some general questions.
In many protcols the running gel and the running buffer is described differently.
1. why do some people add glycerol in the running gel and other not?
2. Should i use the glycin-Tris-buffersysstem or the tricine-tris-buffersystem for my small proteins (8kDa)?
3. Is the difference between the Laemmli and the schaegger+jagowsystem just the ingridients of the running buffer (Tricine instead of Glycine)? Or are there more differences maybe the Gel composition?

i will happy if someone can answer.
trypsin