Stop adding contacts you'll only talk to a couple of times. Are you going to sell something online and the buyer has given you his number to talk to him? It's not a contact you want to stay with, don't add it to your address book. noContact, allows you to write to someone for your favourite messaging app without adding it to your contacts, as easy as that.
In addition, it also provides a useful history for you to have saved. We know you're not interested enough to save it anyway, but you might want to resume the conversation, as easy as consulting the history.

noContact is not a typical agenda, the rest of the applications will not have access to your numbers, you will be in control at all times. Dedicate your time and your phone book to those who deserve it.