Please see this poll: https://twitter.com/davdroidapp/status/1006892001126690816
71 % have voted for keeping current behavior (no automatic selection)
However, to improve user experience, we have introduced a small message to indicate that collections must be selected to be synchronized:
0_1531827957199_Screenshot_1531827779.png
This message is only shown if there are no collections selected when the activity is started.