I personally use /o, but only when it actually means something. In my case the package has a "constant" in a global variable (I'm just not using a `use constant ...`) and the constant is used in a regex. In that case I know that perl is going to keep re-interpolating the variable on every execution and the /o just prevents that. The actual regex wouldn't be compiled more than once because the constant wouldn't change, I just get perl to save some work later.

The idea here is that /o is *all* about interpolation. If you aren't interpolating anything then it has absolutely no point.