You can have the summary buffer sorted in various ways, even though I can't really see why you'd want that.
These functions will work both when you use threading and when you don't use threading. In the latter case, all summary lines will be sorted, line by line. In the former case, sorting will be done on a root-by-root basis, which might not be what you were looking for. To toggle whether to use threading, type T T (see Thread Commands).
If a prefix argument if given, the sort order is reversed.