Knock meter can keep you from popping a motor from lots of things though. Weak fuel pump, clogged filter, bad gas, motor over heating or any number of things that can cause knock. Timing light isn't going to help with anything other then the initial setup.
Timing is crucial with forced induction, but there's no sense not having all the warnings you can.
I used to use this, saved me many times. I highly recommend it to anyone running boost.