Interesting thread but let me add a technical explanation.
A grill will reduce somewhat the high frequencies (around 0.1 to 0.5 dB max) - not worth worrying about really.
Another factor is vibration - when playing loud and pumping loads of air it is possible to make some grills vibrate audibly (as can your furniture and many other things in the room) - again probably not worth worrying about.
Thirdly, some speakers have very sharp corners (which cause edge diffraction) and the grills may be specifically designed to fit snugly over the baffle and reduce edge diffraction by making a smooth transition to the speaker sides. In this case it is important to keep the grills on.
Finally, with the grills removed, the tweeters, woofer and reflex port are exposed and it is extremely tempting to touch or poke these; and the grills offer some essential protection even if they can still be penetrated by hard objects.
A grill will reduce somewhat the high frequencies (around 0.1 to 0.5 dB max) - not worth worrying about really.
Another factor is vibration - when playing loud and pumping loads of air it is possible to make some grills vibrate audibly (as can your furniture and many other things in the room) - again probably not worth worrying about.
Thirdly, some speakers have very sharp corners (which cause edge diffraction) and the grills may be specifically designed to fit snugly over the baffle and reduce edge diffraction by making a smooth transition to the speaker sides. In this case it is important to keep the grills on.
Finally, with the grills removed, the tweeters, woofer and reflex port are exposed and it is extremely tempting to touch or poke these; and the grills offer some essential protection even if they can still be penetrated by hard objects.