'Rare case' depends on the point of view ;-) In companies or big organizations this is the default. If there is no possibility to (un)install silently this could be the main argument not to use it.
I'm such an admin and the first thing on deployment of software is to look which installer was used. Therefore I know that inno setup has silent parameters at all. Unfortunately that's my knowhow about inno.
I think it should be possible, perhaps you find something here: http://www.jrsoftware.org/iskb.php</div><div>Or ask the maintainer directly.
