If you're limited by your SSD, one core running lz4 (or zstd) will double your write speed for object files. If you're not writing hundreds of megabytes per second, then you'll barely notice the overhead at that phase while it makes later phases that load the data back snappier.

If everything fits in ram then compression could be postponed.

And for that area in between, where your files don't fit in ram but compressed they would fit in ram, compression can give you a big speed boost.

That's true. I think less memory is often accompanied with less compute. For example "one core running" is 50% of my available compute.