If one installs Overleaf from the repository on a computer, the auto-complete functionality is not included, although it works in the free version provided online by the company (but with other limited functionalities for those not having a paid subscription). For this reason, this add-on is extremely useful for those researchers who rely on LaTex for their work and prefer to use it via Overleaf, while not being able to afford paying a subscription (I know several cases, affecting especially PhD students).