I would say there are lots of advantages to planted tanks:
- A more biologically diverse aquarium (with many more biological processes going on, which leads to better overall aquarium health)
- Places for fry to hide
- Provides bacteria/algae for fry to eat
- Community fish are less skittish, breed more easily
- Plants reproduce, you don't have to buy plastic plants again
- More stable water, better water quality
On the downside:
- There is a learning curve involved
- You need to pick plants to suit the conditions of your tank
- Most stores are clueless about plant needs and have little variety
- High-tech equipment is expensive, if you decide you want more demanding plants
- Some fish will eat plants or dig them up