There aren't many disadvantages to using a raised bed.
The most obvious one is that you have to buy or build one on your own, while a regular garden bed is just there. Additionally, there might come a time when you have to move your raised bed. In this instance, you'll have to disassemble the bed and reassemble it at another spot.
It's also possible for your plants to freeze because of the cold. The best way to do this is by building thick walls. Since the plants are raised, they're much more exposed to both heat and cold!
Lastly, they're not a good option if you don't have enough moving space in the garden. There needs to be some free walking space between the beds, and if you're just planning on squeezing as many beds as possible in your garden without leaving room for walking - your garden won't look as beautiful.