When do we need sharepoint full crawl?

Most of the developers have encountered this question, when exactly do we need to run the sharepoint full crawl? Why does incremental crawl is not enough.

Here are the following scenarios where full crawl is mandatory.

a) Search  service application created  in the farm and configured with content source(Its obvious)
b) New content source added/created.
c) Adding new  managed property/ updating the existing managed property.
d) After CRUD operation of Crawl Rules
d) If  search index  throwing errors
e) The  credentials of  user account that is assigned to the default content access account have changed
f)  Sharepoint Service pack installed

Atleast for  the above scenarios its  mandatory to run  the full crawl else  search does not return the required results :(