The Request Receipt feature is not entirely new, and it's just a way of finding out if the member you sent the PM to has read or not read your private message.
I usually click Ok anyways...then delete those that has been read regularly to save space on my PM account. A moderator should be doing that.
Someone regular like you....read recipts aren't really important unless you think that this PM you send is very important that you need to be sure that your PM has been read.