Only for bubbles, but they definitely help in that area. You could simply have a sump with nothing but the intake and output pump and it would work fine, but the fancier things help
I have a sump with no baffles! I don't have my skimmer running in there but no bubbles from the intake that are causing problems! I am going to have chaeto and use a pond basket for keeping it in place!
I did plan on running a skimmer but I wanted to test using a power head aimed at the surface to see if will dissipate the microbubbles. After my diy canister a few years ago no way am I going to attempt a skimmer.