I'll start by saying I really don't gamble much anymore, but I did gamble TONS in the 80's and 90's.
Back then, games weren't "negotiated" in my area. If you didn't think you could beat someone, you didn't play them. There were plenty of gamblers around, so it wasn't a bunch of meat eaters fighting over the 1 steak.
I love pool, and I was a great player in my area. There was so much action in a 30 mile radius I never had a need to hit the road. I could still make great $$ any night in any bar.
The only time I ever gave a spot was if I already had my opponents $ and just wanted to keep playing, and didn't care if I gave some back, similar to the TCOM "I win, no money, you win, I'll throw you $20".
Fast forward to current times. In my opinion, you give a spot for 2 reasons.
1. You are playing a friend cheap and just adjust back and forth to keep it interesting, since you're not trying to bust your friend anyway.
2. You are desperate to get some $ in play and nobody will play otherwise.
You don't see much "gambling" today, it's more about the art of negotiation.