We see a lot of old VWs. For some reason, owners of old VWs like adding "stuff". Lights, switches, relays.. "stuff".
Generally its a bit of a mess behind the dashboard with relays floating about, wires taped up, all of it just waiting to knock all your electrics out on the side of a Welsh mountain one summers eve...
The thing is, VW arent daft. They know you like adding this "stuff", so if you look on the top of your fuse box chances are you'll see a load of points to add extra relays and fuses should you desire.
Thats what these are for, relay holders and fuse holders to tidy that rats nest up.
Hopefully, if more people use them we wont have more situations where a T3 comes in for relatively simple electrical work and ends up staying here to rewire half the dash :)