@Aerion
Take a look at this topic Create a curved plane surface which dynamically changes its size and posts from @hofk there.
Gonna make a new thread for this.
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Is there a demo?
Csg dynamically subtracted? Does it not get stuck?
@qifei
Are you trying to create a trail behind your object? If so - there are better ways to do that.
Something like this?
Thank you.
We tried several approaches (realtime geometry creation / manipulation) to solve a similar problem - at least I believe it’s similar 
the logo-animation on our freshly released (micro)website https://cream.gmbh 
(we’ll showcase it here in the discourse soon).
The only thing that performed smooth enough for a complex geometry such as our curvy logo (especially on mobile devices), was animating the transparent material’s alpha-map.
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use localClipping can growing animation
Did you use a VideoTexture for the alpha map?
No, just by tweening a specific (in our case “x”) offset value of the texture (alphaMap), see three.js docs & three.js docs
The 3d-model needs to have a proper UV-layout for this.
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That is a good solution. With the proper setup of alphaMap and geometry UVs (crammed together in one half of the [0,1] interval on either U or V, I guess), the only update you have to do during animation is a single uniform, which will be updated anyway as a consequence of the presence of a texture (actually, the texture and associated uniforms must also be considered costs of this method).
Is there not something called morphtargets that would be good to mention here.
https://threejs.org/docs/#api/en/core/Geometry.morphTargets
Otherwise you need a procedural way to regenerate the mesh per frame or pre-generate the mesh data for switching to per-frame.