Given the choice, would you prefer members to visit frequently, but for a limited amount of time, or members to visit infrequently, but for a long period of time.
Or to rephrase the question, do you want members to visit often or spend a lot of time on the site?
The answer is both, obviously. But let's assume you have to prioritise one.
Most people say the latter. They value time on site over the number of visits. The more time members spend on the site, the more engaged they are. The better the community is.
I'm not sure that's true.
I'd value a member visiting 30 times a month for 1 minute over a member visiting once per month for an hour.
This is because of habits. A high number of visits demonstrates the community has become a habit for participants. People visit an average of 5 to 7 websites per day. It's difficult to make your community one of these sites, yet this is the goal.
You want members to visit often, very often. You want visiting your community to become one of the things people do when they open a web browser. You want members to visit to see what's new in the community. Sometimes they will find something they want to respond to, sometimes not. This is fine so long as they keep visiting.
The tactics you would use to increase the number of visits aren't the same tactics you would use to increase the amount of time members spend on the site.
We should design community sites in anticipation of short visits. Sure, some people will want to read the archives and every scrap of information. Most, however, will want to check, see what's new, and decide whether they need to respond.