More buckets adds more buckets to Minecraft made of different materials with different capacities. While a regular bucket can hold 1 bucket worth of fluid, the Diamond bucket can hold 8.
The buckets added by this mod can be used in crafting recipes in place of regular buckets. With the added capacity, crafting using fluids is now much easier.
The buckets in this mod can be used as a fluid tank and are compatible with any Forge fluid handlers.