Suze is mistaken, TSA lock is not just for within the US, it worked for me in Frankfurt - a notice left behind inside told me that it had worked, been opened and closed just fine without breakage.

I also bought the TSA strap (from Samsonite's company store in Denver) with the lock that you can reset to any number yourself - it is a bit clunky but worked on a suitcase with flush-fitting latches that I cannot lock otherwise these days.

use plastic ties for a little bit of security. Don't use TSA locks even for inbound flight. I assume my TSA lock was cut through Frankfurt transfer. They are OK in the US. But for transfer in Frankfurt, they made us go through security, body search again. So I assume the luggage went through a similar process. They were missing when I got to Italy

Going to Eastern Europe in May. This lock thing has me baffled. Why put plastic ties/cables on the bag if they will be cut off by TSA?

They might or might not be cut off. If they aren't cut off, then your luggage is secure against accidental opening or "casual" dip and go theft.