The drivetrain is a major factor in both riding and maintenance. The chain, cassettes and rings typically need replacement several times over the life of the bike. Normally you'd get exactly the same components each time. The basic drivetrain determines what type of chain, and cassettes you need. You are also constrained by the deraileurs and shift levers on your bike.
On several of my bikes, I eventually switched to different drivetrain. eg: Different numbers of cogs, different crankset, different deraileurs.