The disadvantage of overthinking is, your attention is fixed more than you actually need on your thoughts, and meanwhile you are missing other aspects of the present moment.
The mind always tries to find happiness according to the existing conditioning you have identified with, when you identify with the content of your mind. If you find and keep focusing on the source of happiness within you deeper than the mind, the mind will calm down, because it will be satisfied with this happiness.
Deeper than the mind is an energetic center called the Spiritual Heart. From this center, the flow of Divine Love enters the human system. Learning to find and focusing on this center will have a great calming effect on the mind, and if you maintain it throughout the day, it will lessen the occurrence of overthinking patterns in time. When you gaze away from the Love in your heart, the mind will resume its seeking patterns again, and overthinking will start to increase. Focusing on Divine Love hastens the healing process/growth of a person and a person learns to be happy as themselves, and the mind does not need to seek happiness outside any more by overthinking because it is already being experienced.
These 2 articles are explaining the process of doing this and the different aspects related to this (packed with accurate and concise info), and the third article is a road map to achieve mastery in controlling the mind. (Can also be expressed as awakening to your true self and living with this awareness)