I'll jump in with some perlin noise examples
the way I use the command is first add a /gmask
/gmask [block to replace],
then the perlin command is:
//replace =perlin([NUMBER],x,y,z,.[NUMBER],[NUMBER],.[NUMBER])<.[NUMBER] [block to place]
One of the benefits of it is that unlike simplex, you can use it to place random blobs of just one kind of block (e.g. scattering a bunch of small leaf bushes).
e.g. if you wanted to place noise blocks on top of grass, you could do /gmask [0]&>[grass]
I have no idea what the actual values relate to, but with trial and error you can usually come up with something good.
Best to start with one of these examples and play with the numbers a bit.
In these examples I used /gmask 35:0
//replace =perlin(800,x,y,z,.15,5,.20)<.35 red
//replace =perlin(800,x,y,z,.20,5,.20)<.40 red
//replace =perlin(500,x,y,z,.15,2,.3)<.1 red
//replace =perlin(600,x,y,z,.15,2,.8)<.05 red
it works with mixes of blocks too
//replace =perlin(600,x,y,z,.15,2,.8)<.05 red,yellow
//replace =perlin(100,x,y,z,.12,5,.5)<.75 red
Since as far I know the perlin command can only either create a blob of just one kind of block, or have them all mixed randomly together, I find it best to run variations of the command with different placeholders to stack them together, like this:
//replace =perlin(400,x,y,z,.10,2,.07)<.3 red
//replace =perlin(600,x,y,z,.15,2,.8)<.05 blue
//replace =perlin(100,x,y,z,.20,5,.5)<.10 green
Enjoy