嵌套和继承async/Tasks

我正在开发一个具有async API的PCL(我是本主题的新手(。从我在网上做的研究来看，我对行为和设计含义感到困惑。假设应用程序消耗了一些入口点API，它封装了一些抽象的底层来访问文件。假设此代码正在客户端运行。

public interface IFileProcessor
{
    Task ProcessFile(string filename);
}
public class MyFileProcessor : IFileProcessor
{
    // Adapter can be SomeAdapter or SomeOtherAdapter
    private IMyAdapter _adapter;
    public Task ProcessFile(string filename)
    {
        File file = await _adapter.GetFileAsync(filename).ConfigureAwait(false);
        // Some CPU bound operation
        DoSomeWorkOnFile(file);
        await _adapter.SaveAsync(file);
    }
    private void DoSomeWorkOnFile(File file)
    {
        // do some CPU heavy work here
    }
}
internal interface IMyAdapter
{
    Task<File> GetFileAsync(string filename);
    Task SaveAsync(File file);
}
// Some adapter for a client that has an async API and is mainly I/O bound
internal class SomeAdapter : IMyAdapter
{
    private SomeClient _client;
    public async Task<File> GetFileAsync(string filename)
    {
        // Fetch from server or something
        return await _client.SearchForFileAsync(filename).ConfigureAwait(false);
    }
    public async Task SaveAsync(File file)
    {
        // Push to server or something
        await _client.SaveFileAsync(file).ConfigureAwait(false);
    }
}

但是假设我有另一个适配器，它没有async API，并且它的操作正在阻塞：

// Some adapter for a client that has no async API and is mainly I/O bound
internal class SomeOtherAdapter : IMyAdapter
{
    private SomeOtherClient _client;
    // Don't declare as async since it can't await?
    public Task<File> GetFileAsync(string filename)
    {
        // Read from disk or something
        File file = _client.GetFile(filename);
        return Task.FromResult(file);
    }
    public Task SaveAsync(File file)
    {
        // Write to disk or something
        _client.Save(file);
    }
}

• 尽管存在行为差异，SomeOtherAdapter是否有实现IMyAdapter的业务
• 让IMyAdapter返回Task类型有什么好处吗？假定应用程序调用await MyFileProcessor.DoSomeWorkAsync(...)，那么为什么让适配器为async呢
• 这些操作主要是I/O绑定的，而不是CPU绑定的——这是否会影响我设计这些组件的决策

我知道很难在一个简单的例子中抓住核心问题，所以如果我举的例子太琐碎，无法让我的问题变得清晰，我很抱歉。

额外的问题：如果MyFileProcessor不需要做任何CPU绑定的工作，那么使用async有什么好处吗？