Hi Kirandeep,
These are some limitations of process builder:-
-Process Builders cannot handle before DML It executes after a record has been created or updated. Whereas Apex triggers can handle both before and after DML operations.
-Process Builder cannot handle delete and undelete DML. Whereas Apex triggers can handle all DML operations.
-An error reported in Process Builder is more generic which makes it difficult to find the origin of the error. With -Apex triggers, exception handling can be made more specific.
-It is all or none in case of Process Builder failure. But with Apex triggers partial success is possible.