Horizontal scaling is not a _performance_ tactic, but rather about availability and cost. Having higher availability means trading off consistency, or in other

Horizontal scaling is not a _performance_ tactic, but rather about availability and cost. Having higher availability means trading off consistency, or in other words, using distributed systems. Also, you can not elastically scale vertically, without also scaling horizontally. In other words, horizontal systems are cheaper if you have fluctuations in traffic.