If you make an activeX dll and set its compatibility to "No Compatibility" what effect does that have on the DLL?

in the help it says
No Compatibility — Compatibility not enforced.

i have this DLL that was set to binary compatibility and all was well with it.. but now all of a sudden when i make changes to it.. i need to recompile all the exes that use it in order for them to work properly.. i thought binary compatibility allowed you to just change the dll??