Function Imports - USE

Hi !!

I have been developing OData Services in SEGW and came across Function imports. I went through

https://help.sap.com/saphelp_nw74/helpdata/en/c5/dc22512c312314e10000000a44176d/content.htm

and I still am not clear about it. Could anyone please help me with this ?

Could anyone explain -

• The use of function imports ?
• Why use function imports , when we can implement CRUD operations through entities.
• some scenarios where function imports are used ?
• When to use function imports and when to implement CRUD through entities.