So, I used to know why to call `.nextTick()`, but then @bnoordhuis made
`.setImmediate()` much faster, and I think @trevnorris removed the
problems/limits on recursive call of `.nextTick()`, and I no longer
understand why you would use one vs the other.

Can someone explain why node shouldn't just do `process.nextTick =
process.setImmediate`?

And make some clear statement in the docs about under what circumstances
one should be used, vs the other?

Most reasonable use for deferred callbacks is when returning an EE, and
wanting to give caller a chance to listen on events. Next most reasonable
is when an API is usually async, and you want to make sure it is always
async.

In those cases, is the prefered API now .setImmediate, or is it still
.nextTick?