And not much else, since only a Critical Success lets you control any of them.
You can just cast the Ritual at lower level, and thus easily get Crit Successes, since PF2E has crit successes happen if you beat the DC by 10, not just on rolling a 20 or such.
Take, for example, a Rank 3 Create Undead Ritual, which can create Level 3 Undead. This lets you create e.g. Wighs, or Skeletal Giants.
The Primary Caster has to beat a DC of 27, and the Secondary Casters one of 22, to perform that ritual.
But let's suppose our Caster is level 15 - they have Legendary Proficiency (+8) in the relevant skill, +5 in the relevant attribute, and a +2 Item Bonus to the relevant skill. That means they get +15 to that roll - in addition to their level, so they get +30.
They always make that check, and if they roll a 7 or higher, they get a critical success.
Now, does a level 15 character benefit in combat from having some level 3 minions?
No, of course not - that's the point! If that were otherwise, everyone who doesn't create minions like that would be playing massively suboptimally.
If you want "has an undead minion" to be a core part of your character concept, then there's literary an archetype for that, otherwise the ritual is there to address exactly those complaints about not being able to make undead.
Incidentally, what if you want to have a villain who used the ritual to get some minions, but at lower level?
Well, first of all you don't have to use the ritual, but what if you're a grognard who has to because reasons?
Let's suppose this is a Boss + Lackeys encounter, so there's 6 levels between the created undead and their master. That makes the Master level 9.
Even if we, for some reason, use player stats, we can get Master Proficiency (+6), a +2 Item Bonus, and +5 in the relevant attribute (just gotta use gradual progression). That's +13, plus their level, so +24 - we want to hit 37 in order for them to control the minions.
That's roughly one every 3 attempts, which just means that our Minion-Creator makes two Wights they don't control directly for every 1 Wight they do. And that's assuming they don't perform the ritual in a necromantically desecrated graveyard or such, because that'd alter the DC.