It really depends on what it is you’re trying to share between machines.
I don’t use syncthing but something that fulfils a similar function (git-annex). My Documents repo is set up in such a way that all instances of the repo try to have a copy of everything because documents are very important data and don’t take much space. Other (larger) repos only try to have two or three independant copies; depending on how large and important their data is.