I personally don’t tend to use a lot of writing prompt generators. At this moment in my writing career I have a problem with having too many ideas to pursue. But prompts are part of many writer’s daily writing arsenals, useful for many tasks, practise and kicking our muses into gear.
Here’s a very short post on two LARGE sources of prompts, and a couple more. There are many more out there, so feel free to comment in with your own favourites.