I had the same thing initially.
The upside of async over a simple event loop is, in my experience, when things become less simple, and you end up with hard-to-read little state machines all over the place.
With async, you can have your event loop, but the state machines are handled by the compiler. Code is like threaded code. That can be very convenient.
Threads, obviously, accomplish the same thing, and arguably more easily. But threads have a performance problem when they must interact heavily. Cross-thread communication is expensive. Single-threaded async task interaction is very cheap, comparatively (I use tokio only in single-threaded mode, as an event loop replacement; its multi-threaded scheduler performs terribly on serious I/O). I think the interaction problem is often more important than just the number of tasks.
As for the function coloring argument, I've started to see the async keyword as documentation. A non-async function is "regular logic", it must complete without blocking. An async function is a state machine; as such it must be part of a larger state machine (the event loop), and it can go down into smaller sub-state machines (i.e. call other async functions). If you make that distinction explicit, it all makes a lot of sense.
The upside of async over a simple event loop is, in my experience, when things become less simple, and you end up with hard-to-read little state machines all over the place.
With async, you can have your event loop, but the state machines are handled by the compiler. Code is like threaded code. That can be very convenient.
Threads, obviously, accomplish the same thing, and arguably more easily. But threads have a performance problem when they must interact heavily. Cross-thread communication is expensive. Single-threaded async task interaction is very cheap, comparatively (I use tokio only in single-threaded mode, as an event loop replacement; its multi-threaded scheduler performs terribly on serious I/O). I think the interaction problem is often more important than just the number of tasks.
As for the function coloring argument, I've started to see the async keyword as documentation. A non-async function is "regular logic", it must complete without blocking. An async function is a state machine; as such it must be part of a larger state machine (the event loop), and it can go down into smaller sub-state machines (i.e. call other async functions). If you make that distinction explicit, it all makes a lot of sense.