It's not for sli, it was for maximus which is to link them with quadros. It should also be for linking teslas. It's similar to sli in that the bridge is for the cards to communicate but that's where the similarities stop since it doesn't mirror info. There's not much info on it and it was rarely used. The bridge was also not needed in most cases as it didn't help. Compute usually uses little pcie bandwidth with the gpu being at very high usage most of the time. You'd only find compute purposes that are compatible with this and the majority of people using multiple teslas were writing their own software for compatibility.