Warm-up sets
You want to view warm-ups as a required step before any of your first main lifts.
Then, after completing the working sets of your first main lift, you can determine how "warmed" you feel before beginning the next exercise.
For example, in a program where the main lifts are deadlift and bench press, after warming up properly and performing the working sets of deadlifts, some people will want to do a full warm-up for the bench sets. Others may feel warmed up enough overall to just get right to their working bench sets.
Every exercise does not need a warm-up; you can warm up based on how ready you feel to perform that exercise. Typically, if you take your time and warm up properly including main lift warm-up sets, you shouldn't need further warm-up sets after your main lifts.
We always include warm-up sets just in case: to help individuals who don't have a warm-up routine or are completely unsure how to warm up properly for training. They're optional and there if you would like to use them!
Always consider how "prepared" you are before each exercise. If you ever feel you do need a warmup set or two before an exercise, maybe even just to dial in form, by all means, go for it!