If you have a PRV (Pressure Reducing Valve), or check valve at the meter, then an expansion tank is required.
My last home was working fine without the expansion tank, until they changed the water meter. Then the tank went bad within a few months.
First I repaired the leaks, then two months later it totally failed.
When I replaced the water heater, I added the expansion tank, and I noticed that I had more even water pressure in the house.
That tank has been in there over ten years now.
As far as earthquake strapping, much of it started after the San Fransisco quake.
In the Seattle area, we do it. We also use flexible lines for gas connections on heaters.