haven't looked at them myself but generally you take longer rest periods for heavier sets. The heavier wt you can lift the bigger and stronger you'll get. Too many people focus on building muscle with mod wt and short rest which only builds the crappy plasmic muscle which really doesn't reaslly benefit you any way.
I wouldn't base my training level on how many sets I do. There are plenty of beginners who do 3 sets per muscle but that doesn't make them advanced. An advanced trainer would know how there body responds to each type of lifting (light, mod, heavy), different set / rep schemes etc. An intermediate is generally 18 months of consistent and progressive training. Not just a couple benches and curls each week, but actual periodised training (strength, hypertrophy, power, fat loss etc)