I think it comes with being better able to assess threats, and it probably varies game to game. Now that I'm mildly experienced with these games, I find myself comfortable putting soldiers out in the open in rare circumstances. I feel like there were probably instances of no threat, but I had to go wall to wall just in case. I would make scenarios drag out for no reason just because I didn't want a single soldier ever out of cover. It's funny because back when I first started getting into these games, around the time Enemy Unknown came out, I was obsessive about cover. However if you absolutely 100% know what you are doing there are rare situations where you would gain more by leaving a guy out of cover. But it was also most likely because it wasn't his real save so he didn't care about it and he was trying to move things along for the QL. Or say a reinforcement drop is coming and you want your blademster to welcome some people to the party :DĬonsidering Dan is the furthest thing from a master strategist, he absolutely wasn't doing it out of some genius tactical plan. Or when you know cover doesn't matter, like with melee only enemies remaining and it would get you a better kill chance. However if you absolutely 100% know what you are doing there are rare situations where you would gain more by leaving a guy out of cover, like was already mentioned to say secure a guaranteed last kill you would not otherwise be able to, or get into grenade range that would guarantee further kills and full clears you know, or say you simply have a guy far behind and you just need to catch up into the rest of the squads already secured area. Especially if you are a beginner level player.

Generally, yea, don't leave your guys out of cover.

Xcom 2 quick save