Not necessary to have friend but its fun to have since sometimes gambling with your friend is really adds climax especially after the game you talk about what you activities you have done, also if you win or lose for sure this will be more fun to you especially the sharing part about strategies you used.
Both is a safe place since there are security personnel involve involve or even on online casino and just don't flex your bets or wins then you will be fine upon playing.
I go with that statement, having someone who play with you during your visit inside physical casino adds up the enjoyment, win or lose you and your friend will have something to discuss, either the strategy or the fun experienced that you've got while playing the game, in terms of online casinos, I also agree that to those who love playing discreetly they can just play without any notice to anyone, there's always differences and opinions will be shared in a different point of views.