You don't
have to. But it's advisable. It's both a sim game and a strategy one so micromanaging is pretty much guaranteed to be far more optimal. I've yet to play any kind of strategy game where fully relying on the AI for various management tasks isn't a
vastly poorer choice than doing it manually yourself.
However, that doesn't mean there aren't ways to, well, fake it. All minions have a 'default' room they'll work in, and most of them have a kind of hierarchy of several rooms. Necromancers are a great example — their 'primary' task is to raise ghouls in the crypt. Their secondary is to research in the archive, and their tertiary is to go train in the barracks.
What this means is that a necromancer will first raise ghouls in the crypt until his personal allotment is full, then go work in the archive if there are free spaces. Then, finally, if there are no workstations free there, he'll try and go to the barracks to train.
Thing is... you might not always have corpses in the crypt. This can cause issues, because if, say, said necromancer was dropped into the barracks to train and gets tired/hungry/needs to be paid, he'll stop training, go fill his needs, and then go 'Oh hey, there's corpses available now, better fill up', and once he does that he goes off and starts working in the archive be ause maybe one of your cultists was sleeping at the time, meaning when the cultist wakes up his spot in the archive is filled, so
he goes off to train, and now your suddenly splitting training time between two different minions... etc etc.
Where the specific micromanagement really comes in is if you have that issue and want him to
break that pattern and instead go train
right now, usually because you're trying to speed-level them to lvl 5 so they learn how to raise Wraiths mid-battle.
Otherwise, you should build and manage your rooms with your minions' work priorities in mind. For example, if you only have 3 cultists but a lot of necromancers for w/e reason, don't build a 5x5 upgraded archive (which has 8 slots) if you want the necros to train instead of research, because they'll all end up swapping in and out of jobs a lot.
Oh, and actually, another tip: you can turn
off spawning of specific stuff by selecting each of your gates.
Including the one in your beast den. I actually often build a
massive barracks (like 13x13 or bigger, depending on available space) and either turn Gnarlings entirely off, or just drop them into my crypt (thus killing them and making them necro-fodder) so they don't fill up the barracks 24/7. As far as I'm concerned, if I want cannon fodder, I'll use ghouls, thunderlings, and ember demons
(For those who aren't aware, Gnarlings do actually make decent frontliners, as they have both Cleave and Whirlwind -type moves. But they take
time to rank up just like everything else, and wasting time on them when I could be leveling, say, a pair of Witch Doctors who can
actively resurrect my dying units, powerlevel minions with the XP of the dead, and cast AOE heals, there's kind of a clear winner there
)