This command sets the minimum number of users that must be in a room for the room to be included in the /list command. The default setting is two.
/as security set minlist 3
Generally you will want the minlist to be either 1,2, or 3. If it is set to 1 then all rooms in use will be shown in the list, which is intuitive for users. But many of the rooms will not actually be interesting, and if the list is long, the users will have to weed through it to find useful information. Most users won't want rooms with only one other user. Rooms with two users may have actual chat, but they are also more likely to be personal or dull. Rooms with three or more users tend to be good rooms for chat. But having rooms in the list that are not particularly friendly does not cause many problems, while rooms that are not shown are not going to have more users joining them very often. So setting the minlist too high will make it difficult for new rooms, even good ones, to become popular. As with everything else, it is a trade-off and depends on your priorities.