I use spline caging for all of my foundation modeling. The entire hull plus the basic shape of the nacelles is done with just splines, then I add a surface. If I don't like the shape I'm able to adjust the splines, which means I can see an immediate change to the mesh with a single tweak. As long as I haven't made any radical cuts to the mesh I can keep going back to the splines to make adjustments if necessary. I do one side of the model then, when I'm happy with it, I mirror it to create the other side. I know of some people who use spline caging for everything, while others don't use it for anything. I find, with my particular approach to modeling (which is colored heavily by my being somewhat of a perfectionist), that spline caging allows me much greater flexibility than just messing with polygons and vertices. It's taken me a couple of years to get to this point, and I still learn a great deal with each model that I work on.
Also, bear in mind that I've been working on this ship for almost a year now. It started as a recreation of another mesh I found online, with me using spline caging almost exclusively, and then it gradually morphed until I had completely redesigned the entire ship one piece at a time. Because of that I had to sort of piece everything together as inspiration revealed itself instead of having a single goal from the beginning. That's given me the opportunity to really learn how to manipulate a mesh with ease. My biggest struggle still comes from finding a balance between my desire for greater detail and quality and keeping the number of polygons at a reasonable amount. Fortunately, this one's still sitting at ~15k.