Resting between sets is crucial in order to fully recover after certain sets during weight lifting sessions.  You can usually get through your warm-up sets (up to 75%) rather swiftly with about a 1-2 minute rest between.  However, once you start getting into the 80% – max attempt range, it is imperative to rest 2-3 minutes, maybe even more, to fully recover.  This obviously also depends on the program you are doing because each program has specific goals.  So if you find yourself training by yourself on a platform during your heavy sessions, look at the running clock and make sure you get your rest periods in.  I like to equate it to sprinting because the usage of the metabolic pathway is the same.  If you perform 6 x 40yds sprint intervals pretty fast and only rest 30 seconds to 1 minute between, by the time you get to the 3rd sprint, your time would be very different.  Now, rest 2-3 minutes between, and your tims will be pretty much the same because you allowed your body to recover.  Sames goes for heavy weight lifting.