Some seem to like tubes in the preamp to give the tube texture and solid state in the power amp for better control and let's face it power is cheaper with solid state. Same reason Hybrids are made. When I had tubes I didn't really get a full effect until having tubes in both pre and power amps.

Another consideration are brands, these days stereotypes are being destroyed, you can find tube amps with nice slam and control as well as solid state with a smooth warm sound. Although I've yet to hear solid state give that same type of presence as tubes.

Also, you can change brands of tubes to look for one closer to your taste, this is called "tube rolling". So once you settle on a component you can then roll in & out different tubes for different sound. In fact, there's a company called Musical Designs who has a tube preamp with 4 different boards to choose from, you can buy the other boards and swap them in and out for a different sound.