Joe Obbish looks at time zones:
Queries that use the AT TIME ZONE operator may perform worse than desired. For example, Jonathan Kehayias blogged about performance struggles with AT TIME ZONE at sqlskills.com. One key difference between Jonathan’s opinion and my own is that I enjoy writing these kinds of posts.
Read on for the details and check out some work Joe has done around time zone friendly functions as an alternative to AT TIME ZONE.