the grills

For best sound, listen both ways and decide which you like better.

Grills help protect often delicate drivers. If you have delicate drivers,like soft dome tweeters say, and kids or pets or house cleaners or such running about, I'd leave them on and do something else relatively cheap and easy to tweak the sound if really necessary, like tweaking placement, toeing in/out, interconnects, even (gasp) tone controls if available etc.

My wife and I have 2 "stinking cats" that don't go near my Wilsons.

My dog doesn't go near my stuff either.

Unfortunately, kids and others milling about the house can be harder to train I've found.

Plus, accidents do happen......

I always leave all my grilles on.

The only time my grills are on is when either of my 2 grandsons come over. With my mission/cyrus 782's speakers I couldn't hear any differences with the grills on or off. But I now have Dynaudio's C1's. The soundstage disappears with the grills on and opens up dramatically with them off. Which ever sounds better to you and how important is protecting the drivers are to you.

Some designers factor grill into sound of loudspeaker some suggest removing for best sound. As far as protection most grills will not stop a lab or Child or from pushing in cone. But it does keep it out of site and with kids out of mind. With dogs as long as it doesn't have a smell they like you should be ok. My dogs love the smell of certain drivers they do not damage. But they approach to smell which means press moist noise against cone if you let them. And I don't. My cats where harder on my loudspeakers than any child or dog. Thus today no more cats.