Are Dust Covers a MUST

Dust covers not only keep the dust out but also keep wandering hands away. Many of my customers regretted not having a dust cover on when they lost an expensive stylus to cleaning ladies, kids, pets, or even their own loose sweaters.
I don't recommend keeping the dust cover on when playing, however, as its resonance will screw up the sound (the cartridge picks it up).
Disclaimer: I sell dust covers.
Vinh Vu
Gingko Audio

I think you are asking if one should leave the dust cover on during play or not. I have owned a MMF 7 in the past and never liked the sound with the dust cover on, flipped up or not. The MMF 7 had hinges that allowed for easy lift off of the dust cover. I'd remove it while the table was in use and replace it when I was done.

IMO, it is not a must have for maximum vinyl enjoyment. However, as others have posted there are many excellent reasons to have one. Currently I have no issues with hands of any kind and I haven't had a dust cover for several years. I do carefully use swiffers and microfiber cloths pretty regularly.

The safety factor alone is worth having a cover.

I use a silk scarf to keep the dust off of my TT.

Visitors are carefully manacled and their children are leashed. No problems so far.