This Is How We Do ItThe Worst Mistake Heroes of the Storm Players Make, and How to Avoid ItThis Is How We Do It - RSS 2.0
Third reason: if your death results in the enemy team having a numerical advantage over your team - eg. it's now four blue vs. five red - then you've basically ensured that your team cannot win any team fights and has to play defensively. More often than not, it is a bad idea to engage the enemy when you're outnumbered. So by removing yourself from the game, you're limiting what your team is able to do. By the same token, the enemy team will recognize their numerical advantage and try to press the attack. You're giving them the opportunity to play more aggressively to try to force a team fight.
Should I trade kills?
If you're playing as Murky, dying isn't as bad. Murky respawns very quickly thanks to his egg, and his death only feeds the enemy team one fourth of a kill. If you can "trade" with Murky - by which I mean you die in order to kill an enemy - then that's actually a really good trade. In general, trading is a bad idea. If you sacrifice yourself to kill one enemy team member, then there better be a good reason for that. The only way that is a good trade is if that enemy is more valuable than you, and you will very seldomly find yourself in a situation in which that is the case. Most of the time, if you die to kill an enemy, there is no net gain or loss for either team.
Fighting to the death - don't do it
If you see your team mates dying, don't go die with them. It may seem honorable, but if you want to win, don't jump into a fight that your team has already lost. Don't keep fighting until your whole team is dead.
There are some circumstances in which dying isn't as bad as it normally is, or when it's okay to sacrifice yourself. For instance, Diablo and Leoric have powers that let them return to the fight quicker than most heroes, and while that diminishes the impact of their deaths, that doesn't give you carte blanche to play recklessly and allow yourself to die. That said, if there is one person on a team who will sacrifice himself, that tends to be the warrior. It's not that he's intentionally killing himself; warriors just usually have the best kit to survive - to be the last man standing and hold off the enemy until the rest of his team can escape. The warrior is prepared to die to save his team, but he is still trying to get out of the fight alive as well.
Know when to walk away; know when to run
If you see a fight going poorly for your team, and the warrior starts pinging retreat, then please - retreat. Even if you see him still skirting around, or maybe he falls back a bit and then re-engages, that isn't a signal for you to re-engage with him. He's saying, "Get the hell out of here! I'm holding them off until you can get to safety!" Warriors have tons of health, crowd control, escapes... The warrior is trying to save your team - let him do it. Don't let him die in vain.