There is no acceptable reason behind forcibly freeing the memory GC holds...
(The only possible application when you may know better the state of memory then GC is a single-instance/single-user app... Service is definitely not one of them...)
and... It is a very expensive operation...
and... GC holds the memory because no-one claimed it, because no-one needs it now - so why free it?
Learn about GC:
Garbage Collection | Microsoft Docs[
^]