Just my humble opinion..
Polish for the most part, gives more shine. Glaze
helps enhance polish shine with depth and a often times
wetter looking surface. The main distinction for me is that
a polishing procedure should be done between 1-3 times
a year, while glazing can be done whenever I feel it
can be benificial. On cars that are in fairly good condition
with very light marring, I simply go with a coat or 2 of glaze.
Once the marring becomes more severe, like you can see
it in indirect sunlight, then I go to polish first, then
glaze.