Are drainage holes needed?

[jetflair]

I'm playing around with semi-hydro. Orchid beginner, working with Trader Joes Phals. They all come rotting in densely packed moss, so I've repotted all in LECA and all are doing visibly better.

My confusion is pot and drainage related. I have some in bonsai pots with bottom train holes, some in net pots, some in net pots with an outer pot as a reservoir, and some in mugs with no drainage. I've used a tray filled with water and put the ones with bottom drainage as well as the net pots in it.

I'm frankly confused about how much air circulation and moisture is needed. I'm seeing everyone do the side holes, but if they are not for air circulation, why do we need them at all? Couldn't I use a glass tumbler and eyeball how much water to leave at the bottom?

Will I harm my plant with the LECA in a mug potting method?

Also, should they be allowed to dry out fully between waterings, or not?