Yes. Nothing bad happens to a modern fixture, but you're paying for electricity and shortening bulb life for no real benefit most nights.
People leave lights on for a mix of reasons — a scary house at night, a pet that's afraid of the dark, or just forgetting on the way to bed. None of those are dangerous, so the real question isn't safety, it's whether it's worth the cost.
The answer depends heavily on what kind of bulb is doing the work, since incandescent, halogen, CFL, and LED bulbs burn power and wear out at very different rates.
A single 60-watt incandescent bulb left on for 8 hours uses about 0.48 kWh, while an equivalent 8-9 watt LED uses roughly 0.07 kWh for the same brightness — a difference that adds up fast across a whole house over a month.
Security lighting, stairwells, nurseries, or a porch light for safety are legitimate reasons to keep something on all night. The cost is usually small if it's a single LED fixture.
A motion sensor, dusk-to-dawn timer, or smart plug gives you the safety benefit without the light running when nobody's around. A low-wattage night light (often under 1 watt for LED versions) covers most fear-of-the-dark situations for pennies a month.
Leaving a light on overnight won't damage anything or create a hazard on its own. Swap to LED and add a motion sensor or timer if you're doing it every night, and the cost stops being worth worrying about.
A working lamp with an intact cord and the right bulb wattage for the fixture is not a meaningful fire risk. Frayed cords, loose sockets, or bulbs exceeding the fixture's rated wattage are the actual hazards.
LEDs run much cooler than incandescent bulbs — often under 120°F (49°C) at the base — so overnight use is not a heat concern for a properly installed fixture.
Outdoor lights, especially white or blue-toned LEDs, do attract more insects than warm-toned or yellow bug-light bulbs. Switching bulb color helps more than switching it off.
Yes, by a wide margin. A 0.5-1 watt LED nightlight run all night costs a small fraction of a cent, compared to several cents for even an efficient lamp.