Chunky jumpers suit anyone who's cold most of the year and doesn't want to apologise for it. They're brilliant if you like a bit of structure to your top half, something with actual presence rather than a jumper that just drapes and disappears. Think twice if you run warm indoors, or if you've got a smaller frame and hate bulk near the face, because a dense cable knit sitting right under the chin can swamp a narrow jaw before you've even got your coat on.
If you've none in the rotation, start with a plain knit in a mid weight wool, something like a merino blend rather than pure lambswool, because lambswool looks lovely on the hanger and then turns out to be surprisingly itchy against bare skin after an hour. A crew neck in a neutral, oatmeal or a proper navy, gives you the most to work with. Avoid anything acrylic heavy as your first buy. It'll pill at the underarm within a few wears and you'll end up with bobbles exactly where your bag strap sits, which is the kind of thing you only learn once.
In an ordinary wardrobe, a chunky jumper earns its keep by being the thing that makes everything else easier. Straight leg jeans and boots, obviously, but it's just as good tucked loosely into a midi skirt, because the volume on top balances against something narrower underneath rather than fighting it. Layer a fine cotton shirt collar underneath and let it poke out at the neck and cuffs, it stops the whole thing reading as one solid block of wool and gives you somewhere for the eye to land other than the middle of your chest.
Season wise, this is an autumn through to properly cold winter piece, not a year round one, and I'd be suspicious of anyone trying to sell you a chunky knit for spring. It's built for the weeks when a thin jumper under a coat isn't enough but you're not quite at the full scarf and hat stage yet. It does well on long walks, on train platforms, on any day with a definite chill but no actual rain, since a soaked chunky knit takes an age to dry and smells of wet sheep until it does. Save the thinner knits for layering days and let this one be the whole outfit.
Given time, a good one gets better before it gets worse. The wool softens, the shape relaxes slightly at the cuffs and hem, and it starts to fit the way you actually stand rather than the way it was folded in a shop. Eventually, usually a winter or two in, bobbling starts under the arms and across the lower back where a bag rubs, and that's your sign it's heading towards the loungewear pile rather than the front of the drawer.