TLDR: It is not recommended to use Dropbox, OneDrive or other such file synchronizing software to store or backup Quickmap data, because this can cause data loss and potential performance issues.
There are a number of technologies available to synchronize files and folders to the cloud, such as Dropbox and Microsoft OneDrive. These software packages have the advantage of being able to back up your files to an offsite location (the cloud) in an automated fashion without the user having to remember to do a backup. They also have the benefit of updating the backup copy each time the file it updated.
Unfortunately synchronization has some downsides. Firstly, it’s not suitable for shared databases (such as those used by Quickmap) because changes can be made by one user, which aren’t displayed in another users database because it hasn’t had time to synchronize or the database / software hasn’t refreshed the changed data that is displayed in Quickmap. The second user may then make a change, which is then synchronized back to the cloud, overwriting (and losing) the previous users updates. Secondly, depending on how the synchronization software is set up (for example if the user’s storage is located in the cloud, rather than locally and synchronized), access to the data can be slow, causing Quickmap to become almost unusable.
Therefore, to avoid data loss and performance problems, it is recommended not to use Dropbox / OneDrive to store Quickmap data, which includes the My Documents folder (which contains Quickmap user data), data directories, and any shared data.