A strawman misrepresents an opponent's position as a weaker version, then defeats that. It's satisfying and useless — you've refuted something nobody believes. Steelmanning is the opposite discipline: reconstruct the strongest, most charitable version of the position, including arguments its actual advocates might not have made well, and engage with that.
This isn't politeness; it's self-interest. If your view can only survive against a caricature, you don't know whether it's correct — you just know you can beat a version nobody holds. The practical test is Rapoport's rule: you should be able to state the other side's position so accurately that they say 'yes, that's exactly what I think,' before you criticize it. Most people discover they can't. That failure is information: you were arguing against your model of them, not against them.