Is shielding necessary on interconnects & speaker cables

Your best bet with anything like this is to leave that choice to the professionals. In other words do not look for shielded or unshielded. Don't give it a moments consideration. Look only for what sounds good.

Other than phono cables where the signal is in millivolts so must be shielded its unlikely you'll find a shielded interconnect you prefer. But if you do, buy it. Buy the sound not the theory. Every. Single. Time.

When would shielding be necessary? 

@petware when you know you have a lot of induced noise. :)

Like if you are picking up a radio station, or motors or fluorescent lights.

Thanks Erik, 
i was just curious if certain components like dacs  or streamers or turntables warranted shielding or not as a rule or if it's just on a case by case situation. 

It depends on your situation. I made a 12’ unshielded RCA cable and I have no issues with noise. They sound great! They don’t run next to anything that would induce noise however. You might consider shielding if that weren’t the case.