Default but changeable#
While site to site transit is the default for all multi-site WANs, it need not be used.
If local internet breakout plus software-defined cloud interconnects from the network backbone is more preferable and suitable, then site to site, LAN to LAN networking can be turned off.
Everything but site to site#
Site to site connectivity is not a prerequisite for the rest of the networking stack, so any combination of service edge connectivity is possible, including cloud, colo, ZTNA and other third party connections.
The other option is to have some sites with LAN to LAN traffic allowed, and others without. There is no one size fits all, and multiple hypernet designs can exist simultaneously for organisations which needs more flexible and complex setups.