Isn't it the same thing? When you start the simulation, Blender caches the particledata. But does it matter whether you choose Bake or Current Cache to Bake?
It does do the same thing if the entire animation is already temporarily cached, but if you have any frames missing cache data (if only part of the animation will be played back or some parts got skipped) Bake will fill them in while Current Cache to Bake will not. For small amounts of particles it doesn't often come into play, but for massive scenes requiring lots of memory it can be helpful.