) You don't have privacy or your space
Living with your parents will strip you of your space and privacy and that can be a psychological burden if you have been used to living alone for a long time.
No longer will you have the freedom to walk straight out of bed and head to the kitchen in your underwear nor will you be able to go naked from one room to another. While these were just two quirky and humorous examples, you should remember that you can say goodbye to your privacy and the concept of having your own space.
2) You can't call friends over or have house parties
Have you always been the guy/girl at whose place friends crash every now and then? That could change when you move in with your parents. A big disadvantage of living with your parents especially from the perspective of someone in their 20s or 30s, is that you can't call your friends over.
You can also forget about hosting parties, whether it is a cozy get-together of your college buddies or some of your office colleagues coming over for a round of after work drinks.