If I'm looking for "Tube Sound", why would I put a Tube Pre in front of a SS amp?

I'm purposefully not specifying speakers as I would like to know in general terms the arguments for and against. So, to the degree that speaker characteristics could also influence the choice, please  explain.  FWIW, I do not know a phase angle from an impedance curve so I will try and educate myself as we go along.  Hopefully, others may benefit too.