Is shielding necessary on interconnects & speaker cables

Shielding is a means of preventing RF and EMI from disturbing/distorting the signal within a cable's conductor.  This is far more important in an interconnect than a speaker cable due to the relative power of the signal.  RF and EMI can also be prevented from harming the signal in an interconnect by the geometry of the weave.  SO - simple answer is don't bother looking for shielded speaker cables and either use a shielded interconnect or one with a proven track record of good geometry like Kimber Kable.

A lot of cable designers skip the shield in their cables. Teo Audio, Sablon Audio and Acoustic BBQ are at least three brands that fall into this category. They report the SQ as being more lively. 

Noise vs. capacitance.

Most people are fine with unshielded.
The shield in a cable acts as a capacitor plate, so it may introduce some rolloff, which may be desirable.

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.

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.