Why get an electronic drum amp instead of just a powered PA speaker? Well sometimes it's better to go that route but for most practice situations an amp designed specifically for electronic drums is ideal. The larger models have two satellite speakers to replicate the position of the drums or cymbals when you hit them and can handle even the lowest frequency kick drums. If you don't need as much power or don't have the budget both Roland and Yamaha has some smaller offerings as well.
For loud stage situations a single powered speaker might be a better choice. Give us a call for our recommendations as we test speakers for this use all the time and can steer you towards the right model for your needs and budget.