Precision is a very important part of 2D platformers. Precision platforming lets the player feel and control their jumps, knowing exactly where they are going to land. Games like Super Mario and Rayman Origins use this precision to create tight platforming where the player always feels in control of their character and their platforming actions. So platformers tune their mechanics to be more floaty and loose. This type of platforming is much more frustrating and imprecise than the platforming of the previously mentioned game. This can get very frustrating when playing one of these floaty platformers because it can lead to more accidental deaths and missed jumps because of how imprecise it is.
Sonic CD Edit
All of the 2D Sonic games apply to this type of platforming but I will focus on Sonic CD for this example. Sonic has a very light feel when you move him around. His jumps feel floaty and loose. This can make the platforming (especially in the later levels as the game gets harder and focuses less on speed) very frustrating and annoying as it can be hard to land on platforms and control where you want Sonic to go in game.