What are the requirements for logging SIC time?
You can basically log SIC time if you are a required crewmember and are not able to log PIC time.

So, generally in an airplane like a C-182 which is certified for only one pilot, you can't log SIC time because you aren't a required crewmember.

There are a few exceptions though, like being a safety pilot for the PIC while they are using a view limiting device (like an IFR hood), etc.

SIC time is not pointless because it still adds to your total time! 

As far as landings, you can log them only if you are the sole manipulator of the flight controls, in which case you are allowed to log PIC time (even though you aren't allowed to act as the PIC since you don't have your high performance endorsement).  Oddly enough, in this situation the pilot who is acting as PIC isn't allowed to log it because they don't meet any of the requirements for doing so. It's one of the only situations where the PIC isn't allowed to log it as such.