Since when can you bring coaches on the court?

I saw that Serena brought Richard onto the court a bunch during Miami...I didnt know you could do that.

Can you do that at other tournaments and players have just never taken advantage of it?

If not, why can you at Miami and how come I havent seen others bring their coach onto the court during changeovers?

They've been doing it since last year its supposed to be experimental but most of the top players don't like it serena said she'll use it if her opponent does but she doenst like it

Oh, I didn't know they are doing that coaching thing at Miami. Where will it be next? When will the decision be made (hopefully to get rid of it)?