I have kids so UV or Clear filters are a must. +1 on added protection and +1 that a hood offers as more protection for bumps. +1 on I'd rather clean my filters than the front element of my $2k lens on a regular basis. Why risk scratching or buffing off your lens coating. I would just take off my filters if I'm shooting something critical and put it back on afterwards. Oh yeah some addition flaring may occur with additional filters and of course another layer of anything no matter how good it is will affect your IQ in someway most often negatively but I think the pros outweigh the cons. I also heard that UV filters affects your IQ in someway (color, contrast?) not sure how exactly.