Like a well-motivated ad hominem attack pretty much boils down to an accusation of motivated cognition, a well-motivated attack on tone usually amounts to an accusation of bad faith. While that shouldn't affect your conclusion given a constant set of evidence, it can certainly change your or your audience's weighting of evidence presented and shape the way you approach it rhetorically: if you suspect your opponents might be trying to score political points rather than to present a coherent argument, it behooves you to be more careful in parsing their arguments for dog-whistle phrases or known lines of rhetorical attack. If you suspect them of being deliberately inflammatory to provoke an emotional reaction, that's a good cue to disengage, and so forth.

I don't know how I'd weight this relative to ad hominem, but I don't think I'd call it substantially less relevant in casual debate.