I use them a lot to control the tone of what I write. Since periods can indicate a serious or angry tone[1], I often need some other way to indicate a separation between two complete sentences. For example: "It looks like you forgot to do X; that's needed to do Y." Using a period could be perceived as anger, but using a comma would make that sentence a comma splice. [1] https://youtu.be/fS4X1JfX6_Q?t=3m3s
I wish there were more symbols for other use cases, too. I honestly think the standardization of things in the 20th century actually prevented lots of innovations in language and alphabet. Nowadays, you can't even imagine adding or removing a letter to/from the alphabet. Heck, we can't even change the layout of the current alphabet on keyboards because QWERTY is just too much standardized. In fact, forget about alpha…
These days, I use it to type stuff like (゚ヮ゚ ) ¯\_(ツ)_/¯ and a black box symbol that HN won't let me type, but is eye catching for when you're scanning logs. Symbols like checkmark, ×, the thinking emoji, and the hourglass are useful when taking notes.
Lots can be found in the Windows 10 emoji finder (Win + Period), but AHK is more customizable. Also WinPeriod is juuuuust that much more friction and I find AHK fits into my flow better. This flow shapes the way I think.