a puzzle about start_kdeinit setuid root program in kde3?

[Qin Bo]

hey all:
    I have a puzzle about start_kdeinit in kde3 ,why does it need setuid
root ?
where does the root privilege use ? Is it need to write a root user file or
need to send a signal to
a root process, or the other case ? When I remove the "s" bit at
start_kdeinit, it seems runs ok.
 And why does the start_kdeinit in kde4 needn't setuid root?

-- 
Best Regards,
Qin Bo
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