There's a popular perception in the fitness industry that variety is intrinsically a good thing. Mix it up! Constant variation! Muscle confusion! In the personal training industry, I've found that many clients have the expectation that no two workouts should be the same—that exercises, sets, reps, and rest periods should be changed as much as possible. As a corollary, this implies that a trainer who repeats exercises and workouts is just "phoning it in" and not really putting much effort into designing workouts creatively.
Let's put that nonsense to rest.
It should be so obvious as not even to need mentioning, but repetition of exercises is the only objective way to ensure progress. Variety might be "fun", but dare I say that the purpose of training is to get results first; "fun" is a byproduct and, depending on the trainee, may never even enter the picture (some people really, really hate working out).
A good periodized training program will build in variations in intensity, volume, and accessory work. That's all well and good. My own program incorporates quite a few different exercises, and the intensity (as the amount of weight used) varies from week to week. But I do the same exercises, the same workouts, every week. Is it boring? I don't think so, but that's because I don't think there's anything boring about seeing measurable progress.
Even if your preferred style of training is Hybrid Training—incorporating a variety of modalities for both strength and conditioning—repetition of workouts is vital to structured progress. With a greater number of modalities, the repetition may be less frequent, but it absolutely must occur. If, for example, you did 150 kettlebell snatches for time, it's vital that you record the time and weight and, when you repeat the workout, either increase the weight and/or accomplish the workout more quickly. The workout should be repeated at least every 3-4 weeks.
For basic strength training or Olympic weightlifting, repetition of the basic movements is more important. The goal, after all, is to get stronger at those movements. If your progression isn't planned, if you don't repeat the lifts, then you have no way of knowing if you're actually moving toward your goals.
Good programming, even with a variety of modalities, does not need to be complicated. Progression should be planned through periodization and tested through repetition. When deficiencies arise, accessory work can be added to correct them, then systematically removed from the program as they lose their necessity. Variety for its own sake is detrimental to good programming and should always be avoided. As Mark Rippetoe would say, keep it simple, hard, and effective.