Grounding Speakers


My Tannoy DC8Ti speakers have a ground connector.  Can someone give me a good idea as to why I should use it?  Full disclosure - I had them grounded to my pre amp before.  I just received, assembled, and reinstalled my gear on a new Butcher Block four shelf rack.  My other rack has 3 shelf, so I’m reconfiguring the layout.

My turntable is grounded to my phone pre Amp.  My power amp also has a ground connector.  Should I ground the speakers to the pre amp, power amp, or to a dedicated earth ground?  And is there any reason to use the power amp ground?
128x128oldschool1948
Yes supposedly over time, stranded can develop the so called skin effect distortion etc, at least that is what I've read. Stranded major advantage is flexibility. Solid is a bit more difficult to work with, but is better for a more wide open space, as stranded is better for tighter quarters due to its flexibility. However, it being only the ground wire and not a signal carrying wire, it probably will not have any audible influence whether it be solid or stranded wire. 
Skin effect distortion? I’m not sure that’s true since the signal is not frequency varying. Or is it? Hmmmmmmm...🤔
You can get 14 gauge twisted pair power cord with a shield  (third conductor) This is what Tannoy had in mind. If your cable is not shielded using the ground connector is useless. 
I have 12 gauge copper wire, which is a bit stiff, but I prefer a single strand.

After doing some on-line research and taking into consideration the comments here, I'm going back to what I had before I started this thread:  ground wires run from each speaker to my power amp to my pre amp to create a Star ground setup. 

All of my equipment is connected to a Furman power conditioner, which is connected to a dedicated line.  In essence, I'm following the advice found on the PS Audio site:   
https://www.psaudio.com/ps_how/how-to-practice-best-grounding/

On a side note, I started building my music room a little over a year ago.  I'm in the process of tweaking things, hence the new audio rack. Next steps are to replace my NAD M22v2 power amp, with a much better amp or mono blocks, and then work with GIK on room treatment.  

Setting up a dedicated listening room has been a learning process, and I truly appreciate all of the help and information that I've received and gleaned from this forum.  Many thanks to everyone who has chimed in.