Here's a pretty big bonus for small breasts -- they don't tend to get quite as heavy and sore during that time of the month. Score!
Look, why would you subject yourself to the horror of a high-impact compression bra if you didn't have to? One of the many, many (perky) perks of having small breasts.
Regular bras aren't quite as bad as high-impact compression sports bras, but they're still no walk in the park -- there's a reason why they're colloquially referred to as "boob prison." Since you don't necessarily need the support, why not let your girls run free? It's a personal choice of course, but it's one worth considering if it's something you feel comfortable with.