It MEMS packaging, Au/Sn is perfect for Au-Au soldering. The nature of this alloy allows flux-less reflow and strength that is unmatched in the world of solders.
For high-temp (formerly high-Pb temperature) applications, 80Au/20Sn is the only proper Pb solder replacement. As you would expect – this alloy can also be made in preforms, paste, and other forms to replace high-Pb alloys
For us tech guys, I guess recommending Au/Sn is a little like working at a car dealership and letting people test drive a high-end car. If you’re into solder, it just feels good to know someone is using the “Cadillac” or “Ferrari” of solder – Au/Sn