In earlier Bamboo Cloud versions you need an Amazon WS Account. Because you could only use virtual machines on Amazon EC2 as build agents. There were two disadvantages with that, firstly you had to pay extra money for each build agent to Amazon seconds, you can use build servers that requires special hardwares. With Bamboo 5.10, you can now use your own servers as build agents and you no longer pay to Amazon.
Another important feature is improved Bitbucket integration. You can now see build status of each commit, pull request or branch inside Bitbucket.
With these two important features Bamboo Cloud is one step closer to Bamboo Server Version.