Also to try to avoid having to special-case any logic in terraform etc.
Say you're working on a family of sites for tradespeople like plumber.io, electrician.io, carpenter.io, etc. A fair number of people from India have "occupational surnames" like Miller, Contractor, Builder, Sheriff, etc. Suddenly one Mr. Dev Contractor registers a bucket "contractor-dev" and you have to special-case your bucket names in your terraform.