Usually you deleting your SMS one by one but with this tweak you have.
CleanSMS this option let you delete all of your message once.
Second option: If you have some private message you can hide your messages with one. Click to make invisible and you can unhide them again with one Click.
Third Option: if you aren’t available at this moment and you couldn’t answer on any messages you can put autoReply Messages to say that your aren’t here now.
Options inside Settings.app HAVE FUN!