I think what they meant is requiring that only UTC time should be in the database. This prevents ambiguity when pulling dates/times out as with many poorly designed systems it’s not possible to know whether a date represents UTC time or local time.

At my work we store local time in our database and I hate it. We only serve customers in our country, which only has one time zone, so that’s fine for now. But we’ve definitely made it harder for ourselves to expand if we ever wanted to.