The reason I would argue for always using UTC is that local time in a time that has timezones isn't clearly unambiguous. In fall, when you set the clock back an hour, suddenly the time 02-03 in the morning happens twice. So if you have an event at 02:13, it could have happened at either of the two 02:13's that happened during that night, and since you are using server local time, you won't necessarily be able to know which one afterwards.

Whether being able to figure this out afterwards is important depends on your use case, of course.