There are many different types of swamp in Haven & Hearth, though they are usually only found in small sections. Some kinds of swamps have leeches in them, these attach to your equipment spots and are used to regain health, but make sure you have enough SHP and are not very hungry else you may die.
The other kinds of swamp (murky-water or white on minimap) are useless because you can not build on them, let alone use your boat to travel on it. Thickets (also shown white on minimap) have many trees growing in it and are best avoided, unless you are a great navigator.
Living near a swamp offers a variety of curiosities like Lady's Mantle. New players can use Emerald Dragonflies as an early source of LP. You can also find Candleberries in a swamp.
The implementation of clover has made leeches redundant. It is simple to craft a gauze and heal yourself without the threat of dying from the blood suckers.
If you are a new player living near a swamp,you can heal yourself with Leeches and you can use the leeches for fishing bait.