It does bring up a few interesting tactical choices for avoiding the damage too. Let's say that we're using one of these hazard spells to block off a corner in a hallway. If the spell only applies on turn end, then it's actually much easier to avoid the effects. If you're fast enough, you can just sprint through without a problem, or step in, fire off a ranged attack, and step back out. If it applies on turn start, then same basic principle. If it applies first time you enter on a turn, you can zip back and forth through it while only risking damage once