To run code after the current I/O events in the same tick. It is the standard way to defer work to the next check phase, letting the poll phase process I/O first. Use it when you need to run code after current I/O but before the next timer.
setTimeout runs in the timers phase after a delay. setImmediate runs in the check phase after I/O events. process.nextTick runs before the next event loop phase, even before promise microtasks. Order: nextTick, promises, then event loop phases.
On the next event loop tick, setImmediate usually runs before setTimeout(0) when there are no pending timers, because setImmediate runs in the check phase right after poll, while setTimeout runs in the timers phase at the start of the next tick.
Rarely. It runs before the next event loop phase, even before I/O, which can starve the loop if overused. Most code should use setImmediate or async/await instead. nextTick is mainly for internal library APIs that need to run before any I/O.
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