Tokio included when not using async

[Filip Andersson]

Hello,
when including cached (cached = { version = "*", default-features = false, features = [ "proc_macro", ] })

tokio is also built, is there a reason that tokio is included when async is disabled?
Also how come async is part of the default features?, I would suspect a large portion of people do not use the async features and it would be better to not have it as part of the default features?, reducing compile time, and bin size.

[Filip Andersson]

The reason seem to be because we use tokio primatives instead of std even when async is not enabled? Is there a performance reason this is the case or compatibility?