Have a GMod folder that looks like this?
(https://forums.darkstorm.cc/proxy.php?request=http%3A%2F%2Fi.imgur.com%2Fplmqo6D.png&hash=0d2330bdfc3e1fed1f1164be3d9c46707e664228)
Or just trying to conserve space it doesn't matter, here are three tips to lower the size of your Garry's mod folder.
• Server Files ( Navigation (http://imgur.com/a/9YTeQ) )
Every time you join a server addons get stored in this file, I had a grand total of 958 or around 25GB
• Addons ( Navigation (http://imgur.com/a/dtF0j) )
If you have folder addons also known as "legacy" addons, you can clean out what you don't want. If you have the .gma files, then go in game then go into the "addons" section and uninstall/disable what you don't want. You can also do this from the "Steam Workshop" section in your Steam client.
• Screenshots ( Navigation (http://imgur.com/a/M4Z6t) )
Get rid of accidental or duped screenshots, I don't suggest completely deleting them as there might be some nostalgic value.
(https://forums.darkstorm.cc/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FnFuVvqD.png&hash=9edb76db216b87d1ee656bf99f40dc39c0b89464)
So even though this topic is completely dead i'm reviewing it with some new info while I was trying to cut up some of my gmod space. I found another titan sized folder containing all the maps you've ever downloaded, instead of going to the downloads folder which you can find in server navigation go to download and then maps. Mine was 15.9GB.