I move 10' and tap the ground with a pole. I summon creatures and send them ahead to scout. I mind control foes and use them as cannon fodder.
In "reality", effectively fighting a war is years of boredom followed by 10 second of absolute terror, then years more of boredom. The realistic response to a "the world is as it is" is to spend 95% of every session doing research and preparation, and the 5% of the session to be either a cakewalk combat or an utter disaster.
You don't explore a dungeon. You redirect a river into it, drown the denizens, and sift through the remains. You don't fight in a party of 5 - you gather up dozens or hundreds, even if they are green, because numbers at orders of magnitude matter more than skill and preparation in 99/100 situations.
In "realistic" mode you are either playing a bunch of suicidal idiots, a horror situation of raw desperation where the alternatives are worse, or you are pretending to do something you aren't doing.
WW1's battles that lasted weeks horrified professional soldiers from previous eras. Soldiers used to do a bunch of marching and walking and then had a few short deadly battles, then went home. A D&D campaign is the trauma of WW1 without the situation that makes it at all rational to stay "at the front".
That being said, building a world that makes sense outside of the adventure is fun.
I like tracking organizations in "total CR" units. If the Knights of the Crown have a total CR of 3000, it gives me a world-building hook about how important they are. 200 CR 3 knights each with about 10 CR in retainers and guards leaves 400 CR dangling. 5 or so CR 6 super-knights and a CR 10-ish champion and 3 120 CR armies.
The lich king (CR 20) has 10000 zombies (2.5k CR), 1000 ghouls (1k CR), 500 ghasts (1k CR), 1 deathknight (17 CR), 1 vampire (CR 13), 20 vampire spawn (100 CR), and 100 wights (300 CR) for about 5000 total CR.
If the Knights of the Crown are the entire military force of a kingdom, then they'll be out matched by the Lich King's forces. If they are only a part of it, the Lich King has to seriously scale up to threaten the kingdom.
But having done this work, I can determine what the forces that the Knights of the Crown might send to deal with a problem, and similarly for the Lich King.
In turn this means when I rotate back to world building, the undead fortress will neither have a force that would make defending against it impossible, nor be trivial given how threatening it is.
Also, if a Knight of the Crown's personal guard is total CR 13, it gives me a good idea of what a PC party is impact world-wise. Also, if the players work out how impactful that is, I can drop hints about how dangerous something is using in-world context.
Like, imagine the PCs fight a Knight of the Crown and their guard at some point. Seeing a dozen knights and retainers slaughtered somewhere now sends a real message.