Jersey trousers suit anyone who wants to look like they made an effort without actually making one, which is most of us on most days. They're kindest to softer, looser shapes and to legs that don't want anything clinging at the knee by four in the afternoon. If you want a trouser with real structure, something that holds a crease and reads as formal from across a room, think twice, because jersey will never give you that. It bends with you, which is the whole point, but it won't stand up straight on its own.
In the shop, pull the fabric gently across your knuckles and see how quickly it springs back. A good jersey trouser recovers almost instantly, no sagging pocket shape, no bagging at the knee after thirty seconds of stretching it on purpose. Over months of actual wear, that recovery is what tells you whether you bought well or bought cheap. The better ones keep their shape wash after wash, as long as you turn them inside out, use a cool cycle and skip the tumble dryer, which flattens the stretch out of jersey faster than anything else does. Mine have gone through two years of regular washing and still sit the same way they did on day one, though I did ruin an earlier pair by drying them on a radiator, which taught me that jersey holds a grudge about heat. They don't love being paired with anything equally soft and shapeless on top, a baggy jumper over jersey trousers can tip the whole outfit into pyjama territory, so I balance them with something with a bit of structure, a blazer, a shirt with a collar, a coat that has actual shoulders. Stiff fabrics like denim or tailored wool look odd sitting next to them too, the contrast draws attention to how different the two textures behave.
They come into their own for travel days, for anything involving a lot of sitting, long train journeys, long meetings, long flights where you want to arrive looking like you didn't just sit on a plane for three hours. Autumn and winter suit them best, under a longer coat, with boots, though a lighter weight pair earns a place in a warm climate holiday case too. They're not an occasion trouser, and trying to dress them up for something properly formal usually shows.
What I'd say is worth having a pair that's done the washing machine test more than once before you trust it for a full week of wear.