I program and love block work because it creates scenarios where I can put you in the perfect position and have you work out weaknesses there. The beauty of the blocks is that I can set you up in a ideal position without putting you under tension THEN have you work from that position. The blocks are crucial elements for developing good habits in differing weak positions.
They also allow you to develop strength in weak areas. However, on a regular basis I watch lifters take away the advantage of the blocks by pulling out of the weak position they are supposed to be working and moving to a comprised position because it feels stronger to them. It is important to maintain good position even when starting in a good position in order to gain the greatest amount of benefit from block work. Here is a video of Chance working blocks this morning. Take a look at this to really see what he is missing out on from the blocks.