(Tongue partly in cheek.)
Benefit of taxiing slowly? Takes longer to get there!
Seriously though, there are several situations where taxiing slowly is advised.
On icy or contaminated surfaces.
To provide separation from aircraft ahead to avoid blowback and refreeze of snow or other precip.
Near other aircraft or obstructions.
In poor visibility.
Etc, etc.
In other words, when common sense and good airmanship indicate.
Of course there have been some stories of crew taxiing slowly to send a message to management on a particular issue.
