Unless you try to build a RAID array, you should be fine. However, it is always a good idea to have a backup of any data that you want to be around tomorrow. That way, if the enclosure did mess up the drives, you just restore your backup.
I have this enclosure in both USB2.0 and 3.0 models. LOVE them. I use them to back up the hard drives in my tower and they work flawlessly. You do NOT have to format them (I do not use RAID). Just slide your drives in with or without data and you are good to go!