Dressers are a type of furniture which slightly enhances the comfort of a bed or bedroll (but has no effect on a sleeping spot). To work, it must be placed within 6 tiles of the bed. Small and cheap, there is usually no reason not to attach these to every bed you have.
This comfort bonus stacks with the effect of an end table, but not with additional dressers. Larger beds and bedrolls which serve two colonists at once still only need one dresser. While multiple beds can share a dresser, placing multiple beds in a single bedroom turns it into a barracks, which you ideally should avoid.