Each currency has a minimum amount before your mined amount is confirmed. For instance Bytecoin is confirmed in 20 coin increments but Monero XMR is confirmed every .005. There are also minimum amounts that you need to have confirmed before you can withdraw. Using the same examples, bytecoin is 100 coins and Monero is 0.1 coins. If you're not planning on mining long enough to accumulate the amount necessary to withdraw then there is no point in mining there. It's a good place to get your feet wet when you're just starting out with crypto. Like everything else in life, you have to read the fine print.