why Tris-glycine buffer divided by w/ SDS and w/o SDS? - (Jan/20/2019 )

Hello.

I have a question but there's no answer about this...

In SDS-PAGE, uses Tris-glycine buffer w/ SDS for gel loading buffer. SDS set a charge of protein for negative and Tris is buffering agent, Glycine helps protein move and separation during electrophoresis.

I don't know where Tris-glycine buffer uses and what's different. I thought buying buffer without SDS and add SDS.

Is there situation unfit for use SDS during protein electrophoresis?

The without is usually used in the transfer process, and sometimes for native (non-denaturing) gels.