If it's just for regular maintenance, I wouldn't worry about that screen. I would just change the oil and oil filter. I've never seen one of those screens stop up and if you take the side cover off, you'll have to replace the gasket. Also, there's some clutch linkage parts that will fall out of place and usually the kick starter shaft and the reverse lockout shaft comes out and you have to put all that back. If you're experienced at working on the engine, it's not that hard to put the parts back, but if you're not experienced, it can be a little tricky.
I wouldn't take the side cover off just for that. I never did and I've never had a problem. If I had to take the side cover off to fix something else, then I would clean the screen, but like I said, they're never real dirty anyway.
