With regard to clearness, you need to make certain your dialogue and voice-over are obvious and concise, and make certain the words flow into each other evenly and easily. This stealthily simple audio editing trick will help you achieve exactly that.
Clearly, the main caveat with this particular technique is it is mainly only relevant to voiceovers and dialogue in which the character speaking is off screen or whose mouth can not be seen through the audience - the character whose shoulder we peer in an OTS shot. It might potentially be employed to clean on-screen dialogue in a few instances in which the actor's performance is consistent from decide to try take, but you'd need to be very careful to not throw things from sync.
With this exception - and it is certainly a significant exception - this can be used method to really fine-tune your voiceovers/off-screen dialogue and dial within the perfect pacing and word delivery for audio performances.