The most common issue I see with async programming is that the naive style seen in most samples/docs is strictly slower than standard imperative programming for one user. In other words, it's pure overhead with no benefit at all unless you're at a very large scale and approaching 100% capacity on your hosts.

Most documentation -- and most code I've seen in the wild -- reads like this:

    var foo = await GetFooAsync(...);
    var bar = await GetBarAsync(...);
    var baz = await GetBazAsync(...);

The timeline of that code is exactly same as the standard synchronous version, just with extra steps and pauses.

The following version is more verbose -- which makes it feel slower -- but can provide dramatic speed ups even for a single user by overlapping requests so that they run concurrently:

    var fooTask = GetFooAsync(...);
    var barTask = GetBarAsync(...);
    var bazTask = GetBazAsync(...);

    var foo = await fooTask;
    var bar = await barTask;
    var baz = await bazTask;
   

Unfortunately, I've literally never seen this design pattern in the field...