I was watching a video on Clarisse, trying to understand why folks are using it. It has the ability to import in meshes as instances..

Isn't that the same as Houdini's packing?

Sounds like it to me.

I have heard much good about it, but not sure what the silver bullet about it is, easy to pick up and make stuff fast maybe?

would like to hear from someone with experience to

Hello,

Well it's hard to summarize in few lines, but yes, as you can “only” import data (assets), any duplication (simple copy, or distribution over a point cloud) is instancing. Clarisse shines when you have (or want) to deal with huge assets, and heavy polycount scene. Because the 3d viewport is already using the render engine (cpu), there is no lag or any scene preparation when you switch to the render image. This makes the application very responsive and actually fun to use. Importing, layout and populate multiple houdini terrains (16k*16k) is not a problem; there is not need to use bbox proxy or any other display strategy.

Of course you pay it with the render time, it's not the fastest render engine on the market. But they are doing progress with every release. Running it on a big threadripper should be a very pleasant experience