microC/OS-II and 'thread safe c library' option

This is the answer I got from Altera:

Since "thread safe c library" will handle the synchronization of multi tasks to protect the shared resource, the performance will be lower than non thread safe c library.

If you do not need any operation to protect the shared resource or there isn't any shared resource existed in your application, you do not need to choose thread safe c library option.

My next question is:

But if I use the mutexes or semaphores provided by microC/OS-II for protecting shared resources, then why should I use ´thread safe C library´?

Anyone got a comment?

/S