Fixed duration, fixed units, fixed work, effort driven. How and why and when use all of it?

Dear all,

If I look at it, Microsoft Project effectively has 5 types of tasks (fixed duration, fixed units, fixed work. Plus each of them can be either effort driven or not effort driven, except fixed work, which is always efforts driven)

I  am using MS Project quite for a while, but I could never really understand, why Microsoft effectively has 5 types of tasks, why it is needed, and in which situation use one and not the other.  For my schedules I use most of the time fixed duration and sometimes fixed work.

Does anyone has a good guideline about this?

Regards.

Evgeny