I can’t find it now, but DHH wrote somewhere about optimising for engagement vs action. The idea behind Basecamp is to be a service that helps you manage a project in a faster and easier way, not a service that makes you stay "engaged" while not pushing the project forward. Having more engagement means it’s doing the opposite of of what it's meant to.

This can easily apply for many other services. The purpose of an email client is to surface the important information (filtering and maybe inbox zero?) and let the user act on it (reply and write with the write context). The purpose of a dating website is to find a match and create a connection. The purpose of a social network, on the other hand, is much more debatable.