I personally recommend formatting boot, system, data, and cache before restoring a backup. Imagine an app takes up 10 data blocks with your current setup. The same app in your backup only used 8 blocks (for whatever reason). If this happens to be the last app restored from backup, then there are two residual blocks of data still hanging around, and these can bork the entire system in some circumstances.
It only takes an extra 30 seconds to format all four partitions, so why risk it, just do it.
