I don't have the science behind it such as the hz and stuff, but it adds more range. Essentially, you'd have a mid-bass big, mid-bass medium and a tweeter vs. a mid-bass medium and a tweeter. The mid-bass big eats up more of the sound below "x" hz and adds more depth. If you have a nice subwoofer, you'd have four speakers and the mid-bass big becomes less useful.
Disadvantages: Price. Expect about an extra $200 per door for a good set of CDTs or Focals and that's just for the speaker set with 3 way crossover. You need to also add a Q Logic kick panel or cut-out a place to house the bigger speaker.
My recommendation: Have sub, don't do it. Don't have sub, and not hanging on your car for too long, don't do it. Don't have sub, got extra cash and keeping your car for awhile...sure, what the hell?
better midbass pretty much. more SPL, and better efficiency since each driver has less range to cover, so less rolloff. 3 way sets cost more, and are more difficult to install and vector properly for good imaging. theoretically, the more speakers you have, the more you spread out your point sourcing so that can be a disadvantage.
Yeah, I heard the same thing about component tweeter being too far from the woofer. I have a slight imaging problem because of it. Granted, I have a pretty detailed ear for this stuff...my friends can't notice. I should've just installed the MB's coax style. Now, you're talking three speakers. Great point!
More crossover points and less installation options are the downsides. If you can just barely fit 3 ways and don't have a lot of room to play around with, you're probably better off with 2 ways. 3 ways have more range and lower distortion because the drivers are dedicated to a narrower range. 2 ways offer more simplicity and more installation options, and midbass can still be pretty good. It's mainly a matter of matching what will work best in your vehicle, you can't just cram speakers in there and expect them to sound their best, basically. There are 2 and 3 ways out there and many excellent ones of both types.
yup. I use 3 ways in my Charger, but that ar is HUGE inside, with a lot of open room. I have plenty of space for both drivers and positioning. If I was working with a small coupe, it'd be a totally different story.