I never upgraded my 3 speed Suntour XCT302 I got with my Cycle 7 years ago. It seems to work well and I don't find the need to upgrade it anytime soon in the future but what I wanna know is how do expensive cranksets affect the performance? Initially, I thought it was some marketing gimmick and I didn't bother much but lately, I have found cranksets that are ridiculously priced. I do wanna mention that I am a beginner and I don't have much experience with cycle parts so please forgive my ignorance. Thank you!
In my opinion the most obvious difference with double and triple cranksets is shifting. Front shifting works noticeably better with the stiff chainrings with machined ramps that come with higher end cranksets than cheaper stamped chainrings. I can't write from personal experience, but I've understood that machined narrow-wide teeth hold the chain better than traditional single chainrings.
Of course, it is possible to put nice aftermarket chainrings on cheaper cranks that have replaceable chainrings, but that kind of upgrades are always more expensive than buying what you need in the first place and you miss out on the other fancy features.
Firstly, most people use higher-end craksets, because they enable higher number of speeds in the rear by using a narrower chain. A 7 speed crankset cannot be used, if you have 10 or maybe even 12 (13!) speed chain.
That affects the speed you are going only indirectly. What also comes with higher-end cranksets is smaller weight and stiffer construction. For many people the weight difference is not that big and not worth the money. One can lower the weight more cheaply elsewhere. The stifness is a marginal point to most.
Many carbon fiber frames also require press-fit bottom brackets. That means you cannot use the cheapest square taper bottom brackets that are threaded and therefore the (often) cheap square taper cranksets. The frame of your bike then requires you to go somewhat higher (although less expensive options still exist).