I think what he means is he wants the number of tags to dynamically grow and shrink on the fly given some key combination according to his workflow that day.
A hypothetical example - On Monday's he conference calls with other people in the office and has to use skype and thunderbird and other junk and wants n number of tags. However, from Tuesday to Sunday he doesn't need to have any conference calls and thus doesn't need tags for skype or other crap and so would like to have (n - m) number of tags, where m < n. Recompiling dwm every Sunday night or Monady morning seems like a hassle. I /think/ thats what he means... I think.