In my main HT I need every input / output (and then some) on my Onkyo 886 pre-pro. Ok, a lot of that is to support "legacy" systems / gear, multiple zones etc. but I don't want to give them up / change - so I don't. I just hope that either the 886 outlives me, or, if I decide to change, that something new with at least as much flexibility be available at the time.
But if I ever wanted to slap together a quick and dirty "system" (say to entertain the neighbourhood during my annual Canada Day block party) then all I'd need would be a pair of speakers, stereo power amp, and my iPod Touch. Would need to be VERY careful not to jack up the Touch's output, so I might choose a spare power amp that has level controls and set them to accommodate the Touch's full output without overdriving the speakers. Which sort of highlights one of the benefits of a pre-amp (besides inputs / switching capabilities.)
Jeff