In the late spring and early summer I prefer to use smaller crankbaits. Because at that time of the season a lot of newly hatched fry and other small forage abound. Too large a bait will look out of place and unnatural. Logically, as the season moves towards fall and into winter I gradually increase the size of my bait to keep pace with the naturally available forage which has grown and matured. Water clarity also affects what size bait to use.
Clear water is just the opposite since bass tend to rely primarily on their sight to acquire food.
Also, in clear water, fast-moving baits in natural colors tend to be more productive than do bright colors. Last but not least, always remember a crankbait is nothing more than a tool. How effective a tool it is depends upon you. It is up to you to select the right tool for the existing conditions and then properly use it. Lots of practice, patience, and the ability to recognize when and what adjustments to make are critical to crankbaiting success.