Let me explain,
Mac Auth - Authenticates the device with its mac
802.1x - Authenticates the wireless client (A client who has not received an IP Address yet)
Mac auth and 802.1x are Layer 2 authentication methods.
Captive portal - Authenticates the wireless user ( A client who has received an IP Address) - Layer 3 Authentication
A combination of Layer 3 and one layer 2 method is ideal and secure. Having more than that is not needed hence not recommended.
It just increases the time for a client to get inteded network access if the combination of all the three is used.