What is the difference between Signed Binaries and Launch 1.0?
Signed Binarys simply means that you will no longer have to download and compile the code yourself like you do now.
You will be able to just download the binary package and then run the commands, much simpler and faster. This will also be better for older computers with lower memory since the compilation step takes alot more RAM resources than just running zcash.
And it is a separate milestone from the 1.0 launch, signed binarys can still be mining the Testnet or the MainNet.
The Signed Binaries milestone means that it is possible to produce signed binaries for any subsequent release. (It doesn't mean that the signed binaries produced in that milestone will be the final ones.)
Launch 1.0 includes the actual launch of the production block chain.