That would be the primary, if not only, benefit, but not necessary to achieve that benefit. Remember when Korea was a single nation?
We talk about almost an era ago. I do not know how many European nations have formally declared war on the African countries during the colonization of Africa, I do not think they were reputed as equals, and nobody considered it an affront to international law.
Italy had to do it with Ethiopia but because this was part of the League of Nations (It sounds very DC Comics ^_^), and colonialism was already in decline.
Honestly the idea of the Borg as unthinking machine people with no interest in anything but assimilation didn't survive past the first episode.
It was an extremely original feature for the time, but hard to sustain in the long run I think. If we think of the replicators of SG1 (which have a lot in common with the Borg, they are almost a copy ...) even these after a few episodes have been humanized.
But I'm not suggesting that you could negotiate with the Borg, or sign a peace treaty or whatever. Just that you could deliver a declaration of war before you attacked them.
It would be interesting to know how they would communicate it to them, assuming they did. Subspace? too far (at least until late Voy episodes). Long-range probe? by the time it reaches the Borg space the war could be over.
Perhaps they left the Borg assimilate a diplomat with the news