What benefit is provided by an MCA that is not already provided by an MEA?
MCA is for the fix and specifies the minimal altitude at which a normal climb can clear all obstacles.

MEA is the for between fixes and assures acceptable navigation signal coverage.


source wikipedia.

The MCA can be lower than the MEA of the adjoining route so MEA is required so you won't crash into the next mountain and MEA can also be lower than MCA so it's required so that the pilot can know to climb before reaching the fix so he knows he can get over the next obstacle safely without needing to circle or zigzag to buy time for the climb.