Is shielding necessary on interconnects & speaker cables

Shielding is not needed most of the time as it can hurt the sound.  Shielding can close in the sound and darken it. Now if you need a phono cable from your turntable then shield it! That is the only time I shield with RCA or single ended ICs.  

No need to shield speaker cables. 

its best to not use shielding...closes in the sound.  If you need it, you need it.

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.