Users are limited to mine in 1 account. There are restrictions on the lottery system that mean there is no benefit to running multiple accounts, and rewards would simply be split between these accounts. For example if you mined approximately 60 JSE tokens in 24 hours on one device, if you had 3 running at the same time you would expect to earn roughly 20 JSE on each. Therefore you would simply be using excess electricity for the same result. We want to give users a fair chance of earning rewards and not for the system to become dominated by those with access to the most devices.