Even if not from the perspective of an agile company, or without the need for precise task managament, I'd be careful about over delivering as a constant commitment. I've been overdelivering for years (and not because of my choices, but because I overworked myself) and what has happened is that the "over" part has become the norm (back then), so any time I would state that something is out of reach, they'd point out I'd do my magic and take x days instead - and that's incredibly toxic for a very committed developer.
So my rule is that I will overdeliver if the "over" part is something that aligns with business requirements, is an easy win, or the effort/value is particularly good; and I have the actual energy to do that.
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