It's really useful to see what key pieces of code look like in assembly (though easy enough to do locally), and reaaaaaaaallllly useful to see what they look like across compilers and architectures.

Instead of finding (or worse, building) a compiler or cross compiler locally and doing all the boring steps to compile properly (harder than it sounds) and disassemble the code, you can just splat some code into this and take a peek.

Less about "assembly projects", more about breadth of info available to a developer writing C/C++.

When I used to develop firmware, I would write up the critical inner loops code there and look at the assembly output and tweak the functions to result in better assembly code. Sometimes you can express things a little differently to get around a weakness of the compiler.

Useful way to see how different compilers interpret the C standard. Just code up a minimal example and see what assembly they produce.

i think the primary purpose is to find out what your compiler will do out of your C/C++ program, to see e.g. what optimizations are performed. but who knows, maybe it's also used for actually writing assembly :)

I use it to check things like copy elision etc in my C++.