Some good times to use cited material are:
When you need to defend a point
Cited material can be particularly helpful when you are trying to convince people of your conclusions. By backing up your points through strong sources, you can lend a great deal of credibility to your argument.
When you need to give some background information
If your readers are unlikely to know a lot about your topic, you can prepare them by including cited witness accounts to events, or historical research.
When you want to compare your view points with other scholars
When you are showing how different your conclusions are from someone else's, make sure you mention that other person's conclusions so readers have some idea of what you are rejecting.
When you need to fill some space
Let me explain myself here. I do not sanction sticking in lots of random block quotes just to meet your ten page quota of writing. In fact, doing that is totally a cop out, you are such a better writer than that. When I suggest you fill space, I hope you do it with relavant material. When you get stuck with two empty pages to fill, go back through your paper and see where you can expand on something that will help the overall thesis.
Quoted and cited material can be a great way to do this because including a citation is like making a sandwich. Yes the citation may be a meaty (or veggie) good part, but the bread around it is what makes it a sandwich. Your introduction to the citation and your reflection following it creates a context and also fills you up.