We don't have research on this topic, so it will probably depend on what's simplest for the people installing them, plus budget. When nurseries stock potted roses in spring, unless they are older overwintered stock, they will probably be functionally bare-root, because the wholesalers just potted them up from bare-root into containers just a few weeks prior. Therefore, spring-purchased roses might be basically bare-root whether they are already put in to a pot or not. Generally, mail-order suppliers of roses sell them bare-root as they are easier to ship, and the bare-root shipping season begins earlier than when nurseries stock the potted plants.

Miri