I'm NOT responsible for any errors if you didn't do this correctly.
Only do this on i5 2th gen or better (for desktop) or i5 3th gen or better (for mobile), or i5 U version since 8th gen (for mobile)
Only do this on 5400 RPM or slower HDD, do NOT do this on SSD
Loading times actually degrade on SSD or 7200 RPM Drive on R6S after compression

If you having a 7200 RPM drive, go straight to defrag (Data disk monthly) (at least for r6s compression slows down loading on this game, some games like absolver actually love compression and boost loading time in 7200 RPM HDD)
If you are using SSD, basically this guide is useless unless u wanna save space by compression

Do NOT defrag SSD unless u really need it. It will reduce the lifespan of the SSD
If must, use the solid state defrag, do NOT use any disk defrag

Disclaimer:
-A SSD is always the top notch performance, but this guide made for whoever can't afford to put one on their pc (sample laptop, poor 3rd world nations). Remember that NOT everyone can throw money into new hardware
-A 7200 RPM 100% defragged still yield better result than 5400 RPM with compression + defrag optimization. R6S only compress 2-3 Gb and save that only from launch time but it cost uncompress time so it may beneficial or not depending on the spec. Some games had loading speedup in 7200 RPM with big storage saving, so performance may differ.

1. Compressing the data
(Do NOT use this in system partition disk, if u install steam in same partition as windows, do not compress windows folder, probably just cd to program files or steam and compress all there. If you compressed Windows folder, your Windows won't even boot because "bootmgr is compressed" error).

Run CMD.exe
change dir to data disk/steam (cd command)
compact /c /s /a /f /q /i /exe:xpress16k *

wait till it finishes

2. Download mydefrag 4.3.1(tbh windows defragmenter still works but on slower output performance)
Run Data Disk Monthly on the game drive

wait till it finishes

3. Some games may unfriendly toward compression, like wildlands, so if this actually increase loading times, even with defrag, u can undo the compression to the game by changing the cmd dir to the game and put this uncompress command: (check which games are affected before u do this, all of them so u can bench it).
compact /u /s /a /f /q /i *
then do a disk defrag monthly again with those conflicting games uncompressed, wait till it finish

PS: Wildlands actually crash in the latest build after compression. so if it actually break stuff or slow things down, just uncompress the game that affected and do full monthly defrag again, it should back to normal.

http://forum.notebookreview.com/threads/compactgui-easily-reduce-the-footprint-of-programs-and-games-on-windows-10.809809/

Originally posted by sm2596:

actually if your processor is relatively new, the performance impact should be minimal - in testing that I've done, there's been no noticeable impact on performance. In fact, Microsoft documents the XPRESS algorithms as being geared towards performance rather than compression: here and here
Most CPUs can actually decode faster than they can stream data in from the drive, so for HDDs you might actually see an improvement, e.g.

According to this guy an i7-3720QM can decompress XPRESS at rates between 320MBPS and 720MBPS. That's for an old, mobile chip too, newer ones (especially desktop ones) will be much faster, but let's use these values. An uncompressed file is read at 2000MBPS.

Let's say you have a 1000MB file that gets compressed to 700MB.

Let's now take an average SATA SSD's maximum sequential read speed - 520MBPS. This falls right in the middle of the decompress speed zone of the CPU, so performance might be slightly lower as the CPU might be receiving some data faster than it can decompress it - leading to a stutter.
Uncompressed: 1000MB read @ 2000MBPS across a 520MBPS interface = 1.92s to load
Compressed Worst Case: 700MB @ 320MBPS across a 520MBPS interface = 2.2s to load
Compression Best Case: 700MB @ 720MBPS across a 520MBPS interface = 1.35s to load
Now let's take a HDD, optimistically running at 160MBPS.
Uncompressed: 1000MB @ 2000MBPS across a 160MBPS interface = 6.3s to load
Compressed Worst Case: 700MB @ 320MBPS across a 160MBPS interface = 4.4s to load
Compressed Best Case: 700MB @ 720MBPS across a 160MBPS interface = 4.4s to load

So, even on an older mobile CPU there are benefits if compressing the file on a HDD. Even the slowest decompression algorithm was able to load the file faster than the uncompressed version because the speed was greater than that of the HDD.
On an SSD, it's a bit more on the fence, but still, these are all highly optimistic values.

As for CPU usage - no increases that I could note, even on an SSD, however my CPU is definitely much more powerful than the 3720QM used above. You can see the CPU usage for Photoshop in the original post.

Other users have tested this, and only a 4 or 5 games (out of the 950 submitted) have been troublesome, and these ones might be using virtual disks to store the game on.

after compressing, the data will be HEAVILY FRAGMENTED so do a disk defrag monthly

On heavily fragmented disk, the performance will be REALLY slow
after the Defrag, that's the best i could think of, if you still need more speed, then just buy better hardware (SSD / a high speed HDD like barracuda / WD Black)