It wasn't until I went to the UK in my late 20s that I realized how badly America needs coins in the dollar and two dollar denomination. Having spare coins with weight and mass rather than loose dollar bills helped me get a sense of how many loose singles I had, and being able to drop a couple coins on a counter to pay for cheap items (a bag of M&Ms, a cup of coffee) is somehow, I don't know how, but somehow more ergonomic.
Conversely I almost never carry change in the US and, on the increasingly rare occasions I use cash, I usually just bring the change home and dump it in a bucket. I don't want change that has any significant value.
The US actually has one dollar coins, and it's common for vending machines to spit them out as change. They're the exact same size as the Canadian loonie.
The ergonomics are a real selling point for me. Coins are certainly tidier than bills. They're low friction and hard, which makes them easy to stack, don't vanish in a puff of wind, they're easy to count...
