Do I need IPN for processing preapproved payments?

Do I need IPN for processing preapproved payments?

I'm aware that it's necessary to use IPNs for single payments (situations
when the user approves the payment and than closes the browser etc.), but
am not sure weather I need them for preapproved payments, since the whole
thing is done in a single request. The question goes: can I rely that a
preapproved payment's response is final, or do I need to use IPNs for that
too?
I tried to find some kind of explanation of the whole transaction process,
but without success. Any help is appreciated.
Thanks for any help.