In terms of experience, I've worked for about 20 years in British Columbia. I've worked on a number of drug units around the province, in a couple of different major crime sections, and I have used informants extensively.
The information you receive from them is very valuable. When you start to work with an informant, it's sort of a step-by-step process. So you may get a bit of information, you may be able to corroborate that information, and you may get a bit more. You may end up having a seizure. Usually you can weed out the ones who are less reliable than the others.