I don't think drop sets are optimal for building strength, but can be good for hypertrophy. I think it can be a tool in your arsenal, but I wouldn't use it exclusively. If you really want a combination of size and strength I would recommend using big compound movements (BP, SQ, DL, military press, etc...) for heavy sets of 3-5 reps and then do some assistance work that could include drop sets. For instance, work up to a couple heavy sets of 5 on the the bench press. After that you could do dumbell BP drops sets and maybe drop sets of a tricep exercise. I just wouldn't go crazy with the drop sets and only use them for select exercises.