I think it's important to point out things that you need other players to be aware of, but they might not be. I don't think it's cheap, if you didn't want your opponents to know what you are doing, you shouldn't let ANY of them see it. Otherwise, if I need to tell someone else what's going on to help ME, then of course I will.
For instance, in one large game I was in I was fighting red on one side of the map and saw green was also there to fight him. I drove off green, and green decided it wasn't worth it, so he went after blue instead, and left red and I to fight over that territory.
Well, yellow had no idea what was going on, but while I was stuck in a stalemate with red, green was slowly taking over blue. Based on the log and knowing green and yellow's location, I figured out where blue was and what green had already taken. Yellow/green had 1 border that was inconspicuous, but it was the point that green was about to take a huge bonus from blue on - so I of course told yellow "hey, green is about to double his troops by taking X from blue" to get yellow to step in and stop green.
I mean, maybe yellow already knew, but it's possible that he didn't (all he saw was that green had been fighting all of me, red, and blue, so it's possible he had no idea WHERE these fights were), and if he left green alone, the game was going to take a huge swing in green's favor and I couldn't let that happen - even though I had no way to do anything about it with my armies.
So it was VITAL to tell yellow what was going on, although I imagine green was probably upset that I did so. lol