So I see this "Safe to Fly (Non GPS)" in forum photos on the top of the GO app.

Would it be to my advantage to somehow turn off the GPS?  I am basically planning on using the DJI 3 S to take still pictures of roof tops for inspection purposes.

It needs to hover in a steady position over a roof a near a chimney etc. to take close still photos.

I'm just worried about GPS signal making it wobble or interfereing with operation in a city if I am inspecting a roof.

So is it better to have the GPS on, or is there a way to turn it off, or an advantage to turning it off?

You can't internally disable the GPS, what you can do is stitch to ATTI mode and it won't us the GPS. The "Safe to Fly NON GPS" means that the Phantom hasn't locked into enough GPS's yet, or your in ATTI Mode.
If your wanting to do a roof inspection you shoud be fine in GPS mode if there's clear view of the sky. If your concerned about drifting a bunh then just use ATTI mode and kepp it steady with your stick inputs.
BUT, first I would fly several batteries in ATTI mode until you get totally familiar with the Phantom in that mode. If you get too far away lose orientation in ATTI mode it can make you freak out. If that happens, just switch back to GPS mode and collect your thoughts.

"Would it be to my advantage to somehow turn off the GPS?  I am basically planning on using the DJI 3 S to take still pictures of roof tops for inspection purposes.
It needs to hover in a steady position over a roof a near a chimney etc. to take close still photos".

If you want to hover in place, it would not be a good idea to turn off GPS and use atti mode.
In atti, your Phantom will drift all over the place.
In GPS mode it will hold position.

I'll have to side with Labroides here. GPS will keep your Phantom steady, whereas ATTI will hold altitude, but drift with the wind. The GPS helps lock the Phantom in position. Notice when you are in GPS mode and you are flying, say 20mph, and let off the sticks that the aircraft stops and hovers. In ATTI mode, the aircraft will continue on that course until some force (wind) changes its direction, or it finally coasts to a stop. Hope that helps.

Barney

GPS all the way.  Any wind in ATTI mode and the quad will drift with the wind.  

For the application you wish to use your bird for GPS SAFE TO FLY MODE for stability is the best method giving you more time to concentrate on camera controls resulting in a better inspection/survey video.The two occasions ive done this type of work i found this the preferance

You will need a GPS for sure, however, you only have a single module GPS on your P3S, so it's not going to be as tight as pro or advanced with their double module GPS+ Glonass.  But I think it must be enough, if your shutter is not too slow and the weather isn't windy

Thank you all so much. There are a number of things not explained in the manual or the DJI website. Thanks again.