I've done it to get rid of rusty foliage. The plants start producing new foliage almost immediately. As far as I know, there are no disadvantages to doing this. In fact, it is one of the recommended solutions for the unsightly appearance of rust.

There is one disadvantage to it if you aren't getting rid of rust. The plant uses that greenery for photosynthesis. Can't get nourishment without it. I don't cut it if I don't have to until the first freeze is near.

kay

I did a survey of our daylily society, and the results were mixed. Those who cut down swear by it, and those who don't swear by that too. I say if it's brown, it isn't photosynthesizing anyway, so out it goes. If it's green, it stays up. We are lucky in Michigan that we don't have to deal with rust!