It matters. For example, if Stormfront runs an instance, that instance will be full of Nazis. There's no way they will tolerate anybody else there. Ergo, if you know someone is from the Stormfront instance, you know they're either a Nazi or they're lost and so clueless that they don't realize what all the funny crosses mean.
Stormfront people (again, this is an example) will then sic their userbase on any thread about Judaism. They will intentionally exploit the confusion created by lack of context. They will create threads which users don't realize are transferring them from the world of ordinary humans into the Nazi dimension, where they will be confused and bewildered by the fact that suddenly 80% of their online peers are expressing the kinds of views that are expressed by a Stormfront denizen.
The same will be true when NazBols run an instance and it is already true of the pro-genocide tankies that kbin is already federated with.