DH and I always tip. Always. If there is a tip jar out, it gets our change. At minimum, 20%.
Here is what I learned about tipping, which has held true for many decades:
1. If you are on a business lunch, and someone who is your boss or might someday be your boss, or is close to your boss, turns out to be a lousy tipper, RUN. Brush up the resume and get a new job if that person is your boss. They do not appreciate or remunerate for services rendered and when your annual review comes up, they'll cheap out on your raise, too.
2. Chances are, at some point in life you will be out with a group of friends who may represent an inconvenience to the waitstaff. Maybe your group is so large that they must put together many tables. Maybe out of your group, only two people are buying dinner and the rest are buying $2 drinks, but you're occupying seats that would otherwise turn a decent profit on three-course meals during a dinner rush. Maybe, like DH and his friends, they are all noisy biker dudes who scare other patrons away. Or maybe you need a special favor from the waitstaff, such as finding you a table when it's exceedingly busy and there's a two-hour wait, or perhaps arranging something special for a birthday or anniversary. When you are in this situation, a situation where you are more trouble than you are worth to the restaurant manager, you want to be sure that the waitstaff likes you and is on your side. The best way is to be a repeat customer known to tip well. Restaurants will tolerate anything, ANYTHING, including swinging from the chandeliers, if you are going to buy the entire menu, are courteous to servers, and tip generously.
3. I do not want the people who prepare or serve my food to be angry with me. I was a waitress in high school, and I know exactly what goes on behind kitchen doors when repeat customers who are lousy tippers come through. It's not nice.