[sjnu]

Frees up a gig or two of disk space. Good.

[loeg]

Frees up cheap disk space by moving the library contents to expensive RAM? That doesn't seem like a good thing. And it also doesn't seem possible — you want system libraries to survive reboot. Presumably these files exist somewhere on disk, just hidden.

[plorkyeran]

The dylib cache is stored on disk. It's saving disk space by only having that copy of the libraries instead of two copies.

[loeg]

What would the second copy be?

[saagarjha]

Not hidden, just inside the ROSP partition at /System/Library/dyld.