Yeah, in reality, I tried making a character build based around knife-fighting, but I kept getting killed by people with guns. Guns are so OP in reality. The devs really need to nerf that.
But more seriously, there are three benefits to realism.
First, verisimilitude, which is an important aspect of the game as a whole, is that players should be able to feel that they understand the world as though it were their own. It's a magic world with dwarves and dragons, but rocks still fall, and minecarts fly through parabolic arcs if launched off a ramp, and fire is still hot, etc. The game gets silly and "gamey" when you have things like atom-smashers or magma stacks in wooden reservoirs where the magma never cools, and supporting whole fortresses on crocodile eggs because crocodiles don't need to eat. Those are immersion-breaking aspects of the game.
Second, intuitiveness of controls, which is related to the first, people don't intuitively assume you can block magma with a wooden door or atom-smash infinite quantities of material with a drawbridge. If you can assume, however, that you need food to eat, and you get that food from a farm, and that farm needs to have fertilizer to be able to sustain growing food for more than a couple years without diminishing returns as you deplete the soil, then you are introducing complex mechanics that, at the same time, players are going to be able to understand pretty easily because it's based on the reality they already know.
Third, you have the ability to have Tangential Learning. If you come across things like limestone, chalk, and marble as flux in DF, you start learning some properties of real-world chemistry and geology, even if only on accident. If you want to learn more, there are links to wikipedia articles just waiting for you. Though not so many people actually enjoy it, there is a real joy to be found in some people finding some new thing they never knew they'd be interested in by discovering some information through a game they like.
The problems with realism typically come up when you put realism as a goal to the exclusion of all other factors.
In this case, a balance of realism and some interface/gameplay mechanics that can be added to reduce the micromanagement aspects should give all the benefits of realism without the associated drawbacks of realism-blindness where gameplay is ignored in favor of realism at any cost.