No, but when you do need to replace a drive, one of the MOST common issues is knocking a different drive connection loose and not realizing it. That can lead to multiple drives being knocked offline, causing all sorts of havoc. Better to reduce the possible failure points when dealing with an array that is already running degraded, because that's when you are most vulnerable to data loss.
As far as drive failure being common, all hard drives will eventually fail, the trick is predicting when and catching it before you lose data. That's pretty much the entire reason for running unRaid or RAID, the fact that drives will all fail if given enough time. Backups are a must whether running unRaid or not, drive redundancy is for uptime reasons so you don't HAVE to restore from backups for many drive loss scenarios. Drive redundancy will not protect you against data corruption or accidental deletion.