What's the disadvantage of accessing register via backdoor

I know in some situation, backdoor access is better than frontdoor. But can anyone provide some cases that we it's better to use frontdoor in the test?

In reply to aaaaaa:

It’s not a question of which is better. Backdoor access is a shortcut to improve simulation performance when you repeatedly need to access a register/memory. At some point, you must verify that the frontdoor works.