As a Roblox developer, it is currently impossible to make smooth curves with NumberSequences beyond the current limit of 20 keypoints.
Currently there is an undocumented restriction where NumberSequences cannot have more than 20 keypoints.
This prevents me from having smooth curves to enrich the visual effects of ParticleEmitters (Transparency & Size), Trails (Transparency & WidthScale) and Beams (Transparency).
Below are images displaying situations where smoothening out a NumberSequence to make it feel less jaggy are possible, and where it’s not possible.
Situation of a possible smoothening of a NumberSequence 
This image displays a NumberSequence that will end up having 10 keypoints. This is already halfway to the limit, and still seems somewhat jaggy. Note that the blue line is what we’re focusing on here, which displays a preview of how the NumberSequence will look when applying the spline effect.
Situation of impossible smoothenings of a NumberSequence 
These two images displays situations where NumberSequences cannot look like the blue line. It simply has too many keypoints, making it impossible to make the size of your particleemitter feel dampening or having the transparency of an effect not feel like it’s hitting some spike and then going down all of sudden.
This illustration uses 27 keypoints, which is above the limit of 20
This illustration uses 60 keypoints, which is above the limit of 20
If Roblox is able to increase the limit or entirely removing it, that will allow developers to create less jaggy outcomes when using NumberSequences, and in turn make their game effects appear more pleasing experience. 
