The space taken up by the basic user info is minimal, so saving space is not an issue. And just because a member doesn't have posts doesn't mean they aren't coming back and reading. Even if some only comes in to ask a "what's it worth" question and never return, their post (and hopefully some good, useful answers) will remain to help the next person who searches with a similar question. We would never dream of trimming away all those informative posts just because the member moved on after getting answers. We also like to look at the number of members as an indicator of how many folks our site has "reached out and touched" over the years, even if in some cases it was only for a day.