All it does is increase the RAM usage to the point where it never seems to run out, but most modern systems don't really use / read the system.ini anymore so the performance increase wouldn't even be noticed at all.
Windows will always become sluggish over time a good clean out of unused programs to free up space can help marginally but an SSD is really the only way to get a real performance boost.
Wherever possible you could put programs that have a portable version onto a USB and run them from there (freeing up some space)