A pocket-spring mattress features a layer of coiled springs topped with either foam or natural-fill padding.
Pocket-spring mattresses tend to be the firmest mattresses and the most bouncy. This can make them the easiest to change position on and make getting out of bed easier as your body doesn't sink into the surface as it will with a memory foam or hybrid mattress. That firmer surface is also great for front sleepers.
But, those same qualities can mean that you'll encounter increased motion transfer on a pocket-spring mattress as without the dampening effect of a memory foam or latex top layer a partner's movement is more noticeable, so you might find there's more sleep disturbance if your sleep partner fidgets.
If you're a side sleeper then you may also find the sleep surface a little too firm, as it doesn't offer the sink-in factor to cushion hips and shoulders that a pillow-top, hybrid, or memory foam mattress does.