It doesn't really matter in strikes and other pve missions, but the only pvp mode, (control) completely hinges on which team has the greater k/d on average. Objective pushing only gets you so far if you aren't getting the kills to back it up. In some competitive game modes, it's easy to say it doesn't matter, but control isn't domination, it's team deathmatch with score multipliers. If your crucible kd is below 1 in a match, you were probably a liability to your team.