Those pet water fountains with the disposable carbon filters— are the filters worth it?

I’ve got a Catit pixi fountain and been using the filter, switching out regularly because…why not? But it occurred to me that maybe it doesn’t do all that much (?) and may even do more harm than good (?) with bacteria & stuff having more surface area to cling onto. Thoughts? Do you run them with or without filters?

What if a pet owner (not me) often goes too long between cleanings, do you think it’s better to run it with or without the filter then? A friend of mine it is not as vigilant as I would be with cleaning it so I’m wondering about advising her to just skip the filter. Or maybe that’s even more reason to use one.

Maybe none of this matters and I’m just a crazy cat owner!