In short, when you're dealing with a performance sensitive application they can be helpful to make it blazing fast. When you have a piece of code being executed many times they can be helpful since micro-optimizations start mattering then, too. For the same reason most of us don't write in assembly, most of us probably don't need it for our applications, we're free to waste, but besides being fun/interesting the practical applications where bit hacks can be beneficial do indeed go beyond your short-list. (Game engines (physics, graphics, AI, networking) and databases are two more general topics I can think of off the top of my head, compression is another but could just be a special case of databases.)
Comments
I bookmarked this comment since it more or less answers that question: http://news.ycombinator.com/item?id=3452869
In short, when you're dealing with a performance sensitive application they can be helpful to make it blazing fast. When you have a piece of code being executed many times they can be helpful since micro-optimizations start mattering then, too. For the same reason most of us don't write in assembly, most of us probably don't need it for our applications, we're free to waste, but besides being fun/interesting the practical applications where bit hacks can be beneficial do indeed go beyond your short-list. (Game engines (physics, graphics, AI, networking) and databases are two more general topics I can think of off the top of my head, compression is another but could just be a special case of databases.)