The carseats that snap out of the base are so convenient. You can bring the whole thing into the store with you and put it into a grocery cart when they're too little to sit up in the cart themselves. Or you can bring the carseat with you into restaurants when they're too little for a highchair. This keeps your hand free to eat while baby plays or sleeps.
But if you're saving money by getting the convertible carseat to begin with, you can always use a sling to carry your baby around in stores and restaurants. This is especially good if your nursing. The one inconvenience is that a sleeping baby will almost always wake up when being transferred from car to sling.
As for the stroller that the carseat snaps into, we barely ever used ours, so that for me was a waste of money. Good luck with your new baby!