If ever your party takes it into its head to visit a swamp, you can make life very... ah, interesting for them if your swamp denizens have access to the spells herein. A spellcasting character who lives in a swampy area or came from/studied there might also wish to incorporate at least some of them into his spellbook, although many are not of much use if you are not in a swamp at the time.
Others however - like a huge array of fog effects - will come in handy wherever you are. Fancy a boiling or freezing fog, or one which has soporific effects on characters trapped in it? Or maybe you'd like to be able to relocate yourself from point to point within a fog bank... all these and more are here.
One of the most useful is a 0th-level Druid spell, Stepping Stone. This brings a solid foothold into existence just where and when you need it by causing a stone to emerge under your feet to give you somewhere to stand. There have been times when poking around in swamps when I would have found that useful!
Most of the spells will be splendid if you are running a swamp-based adventure, all manner of effects to throw at the party that both fit their surroundings and which will be totally new to them. It's almost worth writing a swamp adventure to try them out!
[5 of 5 Stars!]