I strung a single line of lights along the beam over my kitchen window one November, mostly to cover up a crack in the plaster, and ended up leaving them there year round. That's the moment it clicked for me. Not Christmas, not a party. Just a plain kitchen beam on an ordinary Tuesday, and suddenly the whole room felt like someone lived there on purpose.
Getting the length right matters more than people think. Measure the actual path you want the lights to follow, not the straight line distance, because lights that drape or weave need extra length to account for the dips. I like to add a good quarter more than my measurement so there's enough slack to swag gently rather than pull tight like a clothesline. Too short and they look stretched and stingy. Too long bunched up at one end is just as bad, it looks like an afterthought rather than something you meant. Count your outlets too, or make sure you're working with battery packs, because nothing kills the effect faster than a cord running across the floor to the one plug in the room.
Where they struggle is in rooms that already have a lot going on overhead, a room with a busy pendant light, a ceiling fan, or exposed beams covered in other hanging things. String lights want a bit of visual room to breathe, so a ceiling that's already cluttered just turns them into one more thing fighting for attention. They also don't do much in a room that gets strong daylight most of the day, since the charm is really an evening thing. A sunny home office isn't where these earn their keep.
Where they sit well is almost anywhere ordinary. Along a headboard in a bedroom, looped loosely rather than taut. Around a window frame in a living room with plain curtains, nothing patterned competing for the eye. Tucked into a bookshelf next to stacks of paperbacks and a few plants. On a porch railing with a plain outdoor rug underneath. They pair easily with wood, with plain painted walls, with linen and cotton throws, because the lights themselves are the detail, not the backdrop.
Before you buy, measure twice along the actual route the lights will take, including any sag, and round up rather than down.