If you run RAID 10 on a busy system and a disk fails, everything keeps running at full speed until you replace the missing disk and rebuild your redundancy.

If you run RAID 5 or 6 and a disk fails, suddenly every read operation becomes several times slower because the missing data must be computed from the parity and remaining data channels. If your normal day-to-day load on the storage is too high you are screwed until you rebuild your missing disk.