This is "allan's perspective":

A frag should be large enough so that should the frag start to do poorly it can be fragged with an intent to save the specimen.

In other words, if it's a two inch frag of some SPS and then it starts suffering in your tank like tissue recession or similar mishap, you can cut off the damaged area to keep the whole alive. In a 1/4" piece you are limited to what you are able to grow should something happen before it's large enough.

Zoas and pallies... IDK. I've had good luck with these so I don't really have a problem with three or four, and have sold three to ten, to include a few that have 20 or 30 heads on them as frags.

Toadstools... I don't frag this guy, it drops off pieces, some are very small some are fairly large. I don't want them so I get rid of all of them. I would say despite the size I wouldn't sell any more of these until such a time that they've grown attached to the rock/plug that I've tied them to. One of the cats on MAAST picked one up from me that wasn't attached and he had problems until he lost it. I would gladly replace that one since it really seems to be my responsibility to ensure that the frag is ready for pick up.

In spite of what ever size I would think that a frag should be attached and growing before getting them out the door. It just doesn't make sense to have a litter of puppies and get rid of all of them before they're weaned... we shouldn't do it with coral.

Anyway, noob opinion here so take it for what it's worth.