A random year inside whatever range you set, whether that is 1900 to 2030 or the whole of the last millennium.
A random year is only useful once the range is right, and the right range is entirely task-dependent. A history prompt might want 1000 to 1900. A fixture for a date-of-birth field wants roughly 1930 to 2010. A trivia round about recent events wants the last thirty years. A worldbuilding prompt might want a span of ten thousand. Because the bounds are free rather than fixed, the same tool covers all of them, and negative values work for BCE ranges, useful for ancient history prompts where the interesting span is entirely before year one.
A year on its own is a surprisingly effective creative constraint. Given 1937 and asked to write something, most people reach for what they know about the period and find they know more than they expected, the technology, the clothes, what was in the news. It works for the same reason a random setting does: an arbitrary specific is easier to build on than an open field. Drawing several at once and picking the one that produces a reaction is usually faster than drawing until you like the first result.
Yes. Negative values are accepted for both bounds, which is what you need for a BCE range in an ancient history prompt.
Yes. Each draw is independent, so a long list from a narrow range will contain repeats.
Roughly 1930 to 2010 covers most adult users. For age-band work, the birthday generator does the arithmetic for you.