Jep, A room is basically a pub (though you don't necessarily subscribe to it by "becoming friends"). The main difference between a room and a pub is that a room doesn't store messages.

• So the room doesn't have to deal with slowly becoming a data-farm, which is a common problem with Pubs.
• The room serves less of an important role as its only function is to introduce peer-to-peer users to each other.

A negative effect is:

• You don't receive new messages until at least 2 people are online
• There is not an initial database of messages that you can grab real fast when setting up your SSB anew

The positive effect is:

• Decreased role of centralized solutions
• potentially a less explosively growing database for people that want to connect over the internet without getting big databases really fast
• on Initial sync (after setting up SSB for the first time) you can specifically pick what other people in the room you want to download data from as the old-fashioned WiFi way of communication applies. This means that you will potentially not download 7 GB of data and freeze your entire client (unless you follow SSB celebs or people with huge friend-lists).

That's just my understanding of it though.