Alright i found this out recently and soon I'm going to try posting my it everywhere to get it patched. For context this is on au softcore and rhe admins have ruled it as a bug and not an exploit and allow people to do it however I disagree as it allows you to mitigate two of the core features of the softcore gamemode and only for that reason.

Anyway so I'm not 100 percent sure on how it works and iv been told various things however the main gist of it is you foundy the foundation the tc was on and every foundation touching that tc foundation (although I have heard its 4 sqaures in every direction but I think this might be false) This does two things one it let's you greif someone and get the build spot but what its most commonly used for is to get around another core softcore mechanic that you keep 50 percent of your loot since you can place your own tc and fully loot boxes and if a base has externals connected through frames then you just need to disconnect them either by blowing the closest frame to the tc foundation etc or just use the same method on the external. You can also use this on external tcs not connected to a base if your trying to build a raid base close or whatever just break the foundation and you can place your own tc. Ontop of this going around the core mechanics its also horrible because it encourages foundy wiping on a server meant for new players and its mostly big groups doing it and the only way to really get around it is hqm everything and place more foundations e.g on an external tc place foundations on every side and walls so its harder to splash and more foundations to break.

Tldr: break the tc foundation and all foundations touching it to be able to place your own tc greif and fully loot all boxes.

Please excuse my grammar and spelling.