What is dovecot.socket and do i need it?

[Hamy]

Helloafter rebooting the server, i keep getting these errors in mail.err :
Apr  7 06:08:09 main dovecot: master: Error: systemd listens on port 143, but it's not configured in Dovecot. Closing.                                                  
Apr  7 06:08:09 main dovecot: master: Error: systemd listens on port 993, but it's not configured in Dovecot. Closing.                                                  
Apr  7 06:08:09 main dovecot: master: Error: systemd listens on port 993, but it's not configured in Dovecot. Closing.                                                  

And then dovecot refuses any connection. the problem is solved if i do a manual restart of dovecot.service.
After some search, i found 2 different solutions, one suggesting disabling dovecot.socket completely, the other one adjusting its settings:
https://sowhatisthesolution.wordpress.com/2015/04/27/upgrading-dovecot-debian-wheezy-to-jessie/http://appbead.com/blog/fix-errors-reported-in-syslog-for-debian-8-jessie.html

I also found an old thread in the mailing list that might be relevant:
http://dovecot.org/list/dovecot/2012-March/134376.html
The errors indeed seem to go away if i disable dovecot.socket .
 I would be grateful is someone could help me understand the role of dovecot.socket , and why that error happens and what is the right way to solve it?
PS: I am using Ubuntu server 15.10 and dovecot package v2.2.18

Best Regards,