Polarizers are always a good idea. They cut down on glare and make contrast a bit more pronounced. You might even want to use a lens hood if glare is a problem. They make you look cooler to boot, you know, turning stuff, having stuff protrude.
I’ve never heard of multi-coat being used to describe a filter by itself, usually it’s “a mutli-coat _____ filter”, and as it usually doubles the price, so I assume it’s a good thing, though I’ve never used one. The coatings are supposed to cut down on flare and other uglies I think.
They aren’t necessary, but it’s nice to know that if a sudden sand storm pops up or children throw rocks at you or what not, your lens will be protected by an easier and cheaper to replace filter.
Unless you’re really anal about image quality, a polarizer is really the only filter that’s going to make a difference that you couldn’t get in photoshop. If people are wearing shiny helmets or driving shiny cars it would be more dramatic, but it can make the sky a whole lot prettier which is always nice.
If the front of your lens rotates you have to correct the polarizer every time you change focus, which would make it pretty useless for fast paced sports I would guess.
I’m by no means an expert or anything, just replying because no one else has.
