Once you make it to the Total Strength programs, you'll notice that week 4 always reads "Deload" for the main lift of the day. What this means is that you'll only be doing your 3 lightest sets for 5 reps each...nothing heavy. It should feel TOO easy.
It's a good idea to take it easy on the rest of your exercises that day too. Do all your supplemental exercises but don't try to break any records.
The purpose for this is to give your nervous system a lighter week to recover. Otherwise, if you push your body hard every training session, week after week, month after month, you risk overtraining, getting sick and injuring yourself.