I think filters are useful as dust / junk collectors, especially modern ones with repellant coatings. The less you clean your real lens the better. The front glass is tough but not airtight so when you clean or dust it there is a real chance of introducing dust or water into the rest of the lens.
Clear filters can’t hurt IQ other than introducing flare or ghosts in backlighting. It’s possible to crack or scratch your front element with minimal to no effect on your picture; a clear piece of glass isn’t going to do anything.
>Clear filters can’t hurt IQ other than introducing flare or ghosts in backlighting.
Or causing fringing, or reducing sharpness, or reducing contrast...
The absolute _best_ that a filter can do to IQ is nothing. But that's basically impossible. Every air/glass interface causes reflections, and no piece of glass is optically perfect. So it's going to hurt your IQ, the question is merely how much, and whether it's worthwhile.
I used to use them. Then I decided I was probably never going to get much of anything reselling my lenses, so I might as well just use them instead of trying to baby them. Haven't had a problem with that decision, but YMMV.
Clear filters can’t hurt IQ other than introducing flare or ghosts in backlighting. It’s possible to crack or scratch your front element with minimal to no effect on your picture; a clear piece of glass isn’t going to do anything.