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> Low power applications. How does latent power draw compare between a 555 and a typical low power microcontroller?

The 555 is very power hungry compared to a typical cheap low-power microcontroller. IIRC there are lower power variants but the 555 still fundamentally does timing by draining current through a resistor, which is going to result in losses.

> I’d naively expect the 555 to be less noisy than a clocked digital microcontroller

TTL ones were exceptionally noisy because the output transistors "shot through" - both output transistors would conduct for a moment shorting the supply rail to ground and crowbarring ridiculous interference onto other parts of the circuit.

And there's another reason not to recommend them - no one sane has used the bipolar version since the Carter administration but they're still out there and it's another pitfall for beginners.

A micro is far superior on both these metrics.