Excuse the scribbled diagrams, this is how we set up the TV studio today. We set up the lights to evenly light the subject, floor and backdrop and used the grid lights and floor lights separately to compare the difference.
The grid set up was a bit quicker to achieve, whereas the floor lights took a little longer to get right as there was more shadows.
I found this video on youtube which backs up what we learnt today –
Green Screen Tips, Tricks and Materials – Chromakey Tutorial
And this video explained really well how to get the keying right in After Effects –
Advanced Green Screen Keying (After Effects Tutorial)