Dropbox and (ufw) Firewall

I'm confused about Dropbox and its use of ports re firewall. Looking at it states that may need to open ports 80 & 443. I've done that in GUFW on my Ubuntu computers but is there really a need to do that? On my non-Dropbox Raspberry Pi on which I have port 80 open (with the router port forwarding 80 to the Pi) implies that no need to do so as Dropbox works Ok on the Ubuntu computers.

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