A choker suits a long neck and a low or open neckline, where there's actually room for it to sit without a fight. If your neck is shorter, or you tend towards polo necks and crew necks, think twice, because you'll end up with two horizontal lines stacked an inch apart and neither one wins.
I reach for mine in the colder months, oddly, when everything else on top is heavier and higher, a jumper or a coat that needs one sharp line near the collarbone to stop the whole outfit reading as one block of fabric. A thin velvet or metal choker does that job in about two seconds flat. In summer, with bare shoulders and a strap top, it still works, but you're competing with more skin on show, so it needs to be doing something, not just sitting there being jewellery shaped. The ones that have actually earned a place in my drawer are a slim black velvet band with a tiny gold bar, and a fine chain one that sits so close it almost reads as a tattoo from across a room, which took me an embarrassingly long time to work out was the point. Metallics in gold or silver are the easiest to live with because they don't fight with anything else you're wearing, they just sit there being quiet and correct. Bright colours and big stones are lovely on their own but they turn the whole neckline into the headline of the outfit, so everything else has to go quiet, a plain top, nothing else near the throat.
This is where I've learned the hard way: never stack a choker with a statement collar, a high neckline with any detail on it, or a long pendant necklace underneath, because your eye doesn't know where to land and ends up landing nowhere. A scarf and a choker at the same time is, I promise you, a crime against your own neck, you will look strangled by accident rather than styled on purpose. I wore one with a roll neck once, for a whole evening, before a friend told me it looked like I'd lost an argument with a cat. Keep the rest of the neck and upper chest empty and let the choker be the only decision happening up there.
It's a small thing, but it changes where people's eyes go first, and that's worth more than the price tag suggests.