if you don't have problems with incompatible software, then is no need for formating; some backup software or partitioning software may have problems with dynamic drives, but if you aren't bothered with incompatible apps, then leave it as it is; Or are you bored?
although only one drive letter mapped to a dynamic drive doesn't make sense; e.g. this partition type is made for self increasing volumes; so you don't have to re-partitioning, if one volume at your second HDD runs out of space;
for more information: left click at your desktop, hit "F1" and have a look into Windows' helpfile;