Tipping started as a feudal custom where the elite effectively would throw extra crumbs to their lessers. Google "origin of tipping culture" for details.
Now it's just a way to guilt-trip and nag customers into padding the profits of restaurants.
But it's practiced mainly in America and neighbouring countries. Most of the world doesn't do this. I know for sure that this isn't common in Europe or in SouthEast Asia, and restaurants there still produce fine food with good service.
It's annoying, and it enables bad employer behaviour.
It's annoying because it now puts customers in the position of employers. The culture has people judging other people for how much they tip now. Paying employees isn't the customer's job. It's also annoying because we can't just take the sticker price when purchasing something; we all have to do more math in our heads to see if the item is in our budget.
So now you see a sticker price of $10, and then you have to add 13% HST on top of that, and then a 20% tip on top of that. 1 * 1.13 * 1.2 = 1.356. So everything in the restaurant now has a near 40% multiplier on it. Annoying.
It's enabling because now employers offer workers lower paying job because "they'll cover it up in tips". And so now it's an expectation that customers pay the tips. And the expectation of this vicious cycle is so entrenched in our society that the government sets minimum wage lower for serving staff. Good job government. And it's not like the NDP or Liberal parties are trying to fix this either; they don't care about the little people.
This is so entrenched that even the workers buy into this. There's plenty of videos online about food delivery workers getting upset at customers who leave a tip that's "only 20%". Ridiculous.
Don't be a part of the problem. Don't pay into a system that shamelessly underpays their workers. Starve the beast, and go buy groceries instead of eating out or ordering in. Cook your own meals; it's cheaper, healthier, and takes just as long, and you wouldn't be participating in a shitty business practice.