Strength training is often viewed as a single thing both in sports performance training as well as in general fitness training. People say things like " I do strength training once a week." or "Can strength training benefit me?" this demonstrates a fundamental misunderstanding of what strength training is and how it is applied.
The NSCA breaks down strength training into several different "goals" which are as follows.
Block style training matches up well with this type of breakdown of training goals. In this style of programming your training cycle is broken up in to sever different blocks that consist of multiple weeks of training. Each block has a specific goal and physiological adaptation that it is trying to accomplish. Take for example an athlete who needs to increase muscle mass and build size in the off-season. Hypertrophy would be a large focus of their overall training program. Their first off-season training block would be with the goal of hypertrophy. As stated earlier, this goal will determine all factors that go into training, length of the block, which exercises, number of exercises reps, sets, rest intervals, etc.
The main advantage of this style of training is focus. Each block improves on physiological trait before moving on to another. Often times strength training programs can try and do multiple things at a time and fail to be productive as a whole. For the athlete example above, the first block is hypertrophy so once progress in that area is achieved then they can move on to the next block which may be something like strength, in which case the goal of building strength will dictate the training variables.
Having a focus allows the maximum amount of progress to be made by allowing the appropriate amount of time for development before variation is added to the program. This should be demonstrated by tangible progress within each individual training block.