In the windows environment, the impact of CPU can be ignored,
It can save 20%~25% and even more disk space,
My harddisk is 1TB
Right now 328 GB is free space. I think that this would be enough for 3-5 years for me.
What is a reason to compress blockchain and increase the work for CPU?
I see no reasons for compressing data on disk.
Fast compression algorithms can trade very slow I/O time, for much faster cpu time - thus speeding things up in general.
For example, if 100 mb can go down to 80, reducing read, write, seek operations, the overall time of a process involving disk I/O on these 80mb can be sped up significantly.
Now if you have a much better compression algorithm that takes 100mb to 60mb but takes a couple seconds instead of msecs to do the job in order to gain the extra -20mb of compression - that doesn't work to speed things up in local operations. It could be still useful though for network transmission because those 20mbs could take more than a few seconds to get transmitted.
Another reason is that if you are marginal with the blockchain in a particular storage medium, especially SSDs, you can then fit the blockchain after compressing it. That will allow you to exploit the faster SSD instead of going with the slower mechanical.
The blockchain won't fit in a 64gb SSD right now, but it can fit compressed (say a BTRFS partition with compression) - although it doesn't have much headroom for SSD operations that require some free space. In some time, it won't fit in a properly configured 120gb ssd running an OS (assuming it has like 40gb for linux, swap, and free space that SSDs require) but it will fit if the data is compressed. The gains there are exclusively from using the faster SSD over the mechanical disk.
In any case, from searching the dev mailing list in older discussions I think some devs are reserved in using popular compression algorithms due to security concerns and exploits.