Yes, you can choose not to sync your family tree with a family site at MyHeritage.
However, Family Tree Builder trees are meant to be synced with a family site and can be best experienced by syncing. If you choose not to sync there are a lot of features that you won’t be able to fully enjoy within the program, such as Smart Matching, Records Matching, Upcoming Events and Profile page from the Family Site section and more.
Syncing also serves as an online backup of your family tree. In case the tree on your computer becomes corrupt, you can easily download your family tree from your family site. This is an invaluable part of syncing that protects your hard work.
To stop the Automatic Sync, please do the following:
Open your Family Tree Builder Software.
Click on ‘Tools’ from the grey tool bar.
Choose ‘Options’ > ‘Sync’.
Change the Automatic Sync settings from ‘Yes’ to ‘No’. Click on OK to save your settings.