bluetooth and wired pentesting and such?

so I am not a pen tester. I am looking at this from a hobbyist point of view. i have not done anything in real life but have watched videos on youtube and such. When i think pen testing I think wireless and a little wired Ethernet pen testing. But have heard that one can do Bluetooth pen testing and sniff Bluetooth packets and such. 

I was wondering how often does Bluetooth sniffing and packet injection etc come up in the real world of pen testing? When I think Bluetooth i think headphones and microphones and such and maybe a keyboard. 

Also is wired pen testing still in high demand or is that becoming less and less?

Thanks

PS I am a noob at this stuff so sorry If my terms are incorrect. Also when you respond can you "dumb" down the explanations.