I don't necessarily know all the advantages to the microed as far as efficiency and such things are concerned but when I started using TB it was -the- editor and I've used it since. It's quick and responsive, that's always nice -- and I love how it reflows text -- I've always had it set with "persistent" selections, automatically reflowing with full justify.
The truth is, though I'm rather comfortable with these settings, they're not of the importance they once were. When Microed was in its prime, it was common for mail clients to have trouble with long lines--sometimes reading, but at the very least with replies having ugly broken lines. Microed rose to the occasion, elegantly wrapping incoming and outgoing mail and was/is fully capable of seamlessly reflowing quoted/forwarded text. Things are handled more elgantly by other mail editors now than they once were, making MicroEd less important, I suppose--but I still have yet to find an editor that handles plain text mail more elegantly.
I've often wished they'd release Microed as a standalone text editor/notepad. No luck there, but The Bat! does now have "Smart Bat" -- a built in notepad/calendar -- jot down notes with it and it can be used to have e-mail messages automatically sent out at certain times/dates. Once upon a time, scheduler saved me face when I'd forget birthdays, it'd still mail them. They'd think I remembered