Controlled round "grabs hold" of the cartridge, picking it up from the magazine and controls and holds it while being pushed forward into the chamber. Push feed is just that ... just giving forward motion to the cartridge as it is chambered.

Some prefer one over the other. It is said by some that in a dangerous game weapon that controlled round feed is better.

I prefer it myself, but for no other reason than the majority of my favorite rifles are Mauser 98 variants and I've just grown accustomed to its characteristics.

With a controlled round feed you can theoretically be upside-down and cycle your rifle without losing the cartridge to gravity. In other words a controlled round feed rifle is supposed to be in control of the hot cartridge and the spent casing from the moment you guide the bolt forward to chamber a round to the last second when you have withdrawn the boltfull back and have ejected the spent round.

I can't think of too many negatives or positives to either. They are just different.