Hello , question , must de wifi on your tablet with the dji go app thats in use with USB on your controller  always be on !!!!!

No. Tablet nor Smartphone must have online services.
Must people also recommend to put them into flight mode during flight.

Less because of the aviation rules more because an incoming call or message can overlay on the DJI Screen and that could cause a crash.

Thanx , today my flymore combo with the red mavic is delivered , i try to do everything the right way

Hi there, just to verify, you wanna know if the WiFi should be turned on when flying the drone, right? If yes, when connecting via the RC, WiFi or internet is not compulsory when flying. Please let me know if I misunderstood it. Thank you.

hello , right , wifi can be off when flying the drone . Only by start up wifi on for cheking possible updates.
Thanx

wifi should be turned off when flying as you describe in yr post. Reason is that wifi and the remote opperate on the same frequency band 2.4ghz - therefore to reduce risk of conflict it is advised to turn airplane mode on which disables wifi and prevents incomming calls which you really do not want when you are flying and especially not when an incomming call happens at the same time the wind picks up and your battery is getting low. Short answer: wifi off unless you are not using the controler and flying using the wifi connection in which case your distance and height is more limited.