If you use Bookmate on several devices, your profile will be updated simultaneously across all of them. In order to successfully synchronise it is necessary to log into the same account across all the devices.
For example, you own a Windows laptop, an iOS phone and an Android tablet. If you start reading on your laptop and make a few quotes, you will be able to continue reading on your phone from the point you stopped at. After adding some more quotes and a couple of new books on your phone, you can switch to your tablet and continue to read from the point you stopped at on your phone, whilst retaining access to all of the quotes and new books which you've previously added to your profile.