I was always building just one base, but on my first A17 game I started doing two bases, because of the rise of difficulty and my base already being damaged by wandering hordes. I wanted to make sure I'll have a ready to go base when bloodmoon starts instead of being inmidst of repairing my base. I also needed less resources that way, as I will explain:
On the flip side two bases means more resources needed.
Imho it's the other way around, at least at early and mid game. In the long run two bases will be more resource hungry, but in the end game resources aren't a problem, in the early game they are the main problem.
Let's just assume I'll find a POI with cobblestone walls, no outer concrete stairs that need to be taken out and a size of 14x14 (the smallest cobblestone houses). Even if I'm just upgrading the middle row to enhanced concrete, it will cost me 840 concrete mix. A seperate 5x5 tower with the bottom three rows made out of enhanced concrete needs 480 concrete mix. I need additional spikes that way, but wood is easier to farm than concrete.
I'll just put a row of spikes around my main base for occasional screamers and have a emergency chest with some food and ammo on my horde base. If there isn't a wandering horde for 12+ hours before a normal night, I'll stay that night on my horde base to avoid getting my main base wrecked.
I add more 5x5 towers to my horde base time by time and connect them. Usually like every fifth day and even faster later on. That way I keep up with the rising difficulty and mid game it's still cheaper than enhancing my main base. At some point my main base gets three rows of enhanced concrete, but at that time I have plenty of it.