www.makemkv.com

I’ve recently started nearing my storage limits and before buying new drives I thought it prudent to take proactive action and go through all my media and mux out audio and subtitle tracks I have no need for. However in almost every single case, stripping foreign subtitles, audio tracks, and commentaries tend to increase file sizes by between 500MB-2GB when using MakeMKV.

My main question is, why? Is there a lot of decompression happening? Even just rewriting the media file with no changes at all leads to larger files.

There is no need to use MakeMKV to just remove tracks from your existing MKV files; mkvmerge from mkvtoolnix can do it.

However, just removing audio and subtitle tracks is not going to make much of a dent in your file sizes, as they're rarely more than a percent or two of the overall size. Using a tool like handbrake to compress the video better will make a HUGE difference... And it can leave out tracks you don't want.