I used to work as a server at a fancy restaurant that did a lot of weird fondue dinners and wedding reception type gigs. These events are massive and the service is distributed over a group of servers, so by the end there's a big chunk of change left as the tip that should be distributed "fairly". At the end of a long night the last thing you want is to deal with the bullshit politics of money distribution. There's always passive aggressive pandering for a larger chunk of the tips by everyone. Servers always seem to think they did more work, bartenders never seem to get enough tips at these events (they really don't, either), and you always want to have something to give to the cooks. I've always liked the cooks at these jobs.
All the drama regarding tips in that setting could have been avoided by charging a 20% service charge on the total bill and allowing the employer to distribute the money. This alone would have made the job less stressful and servers more friendly to one another. I quit within 2 months even though the money was good.
I also tip because of societal convention and nothing more. It's awkward with delivery drivers since, depending on where you bought your food from, you may have to tip in cash and fish in your wallet for bills, which means drivers get a roll of the dice as to what sort of bills are in my wallet. I'd say most get around $5 on avg.