It depends on your company leave policy.
If you sandwich holidays and weekends in between your leave duration, it's called 'covering'.
If you prepend or append holidays and leaves along with your PL, it's called 'clubbing'.
So the options for a company are:
1. Allow clubbing and covering
2. Allow covering but not clubbing
3. Allow weekend covering and clubbing but not holiday covering & clubbing
4. Don't allow clubbing and covering
If you wish to keep your HR administration overhead lower, it is best to have simple leave rules. But if your workforce is large and clubbing and covering is impacting your business, you have no choice but to implement these rules.
These days, web based leave management software (at least the better ones like Greytip Online) let you define your leave rules and automatically enforce them allowing HR to focus on better things to do.