Bamboo's pricing tiers are based on build slaves, or "remote agents" as we call them, rather than on user seats. With multiple agents you can split long-running test suites into parallelized batches, and run multiple builds simultaneously. The more concurrency, the faster your team gets feedback on their changes. The faster the feedback, the easier (read: cheaper) it is to address problems.

One thing to note here is that Bamboo's remote agent pricing is based on the number of agents currently running. If you have installed remote agents on Server A through Server D, but only the remote agent on Server B is running, that will remain within a 1 Remote Agent license. You won't be able to start up the remote agent on Server A while Server B is running. You would need a higher number of remote agents to run builds in parallel, or to leave remote agents running and available on multiple servers. This means that you can install as many remote agents as you'd like, but if you want to have multiple agents running at the same time you'll need to purchase a higher agent tier.

The best way to determine how many remote agents you should license is through trial and error - we offer free 30 day evaluation licenses (1000 agents) that can be used to do just that. You might also find our blog post - How Many Build Agents Does My Project Need? (a.k.a. “The $16,000 Question”) - helpful when deciding on an agent tier.