Rooted devices are more vulnerable to malware attacks. Making changes to the code of a software increases the likelihood of introducing a malware.
Voided Phone Warranty
Rooting your Android device will void your phone's service or warranty. If anything happens to your phone even when it is in the warranty period, the manufacturer is going to charge you for the repairs.
Risk of bricking your device
A ‘bricked’ phone means a dead phone and is the same as carrying around a brick in your pocket. After rooting, you can make any kind of changes in your device, but making wrong changes will result in bricking your device.