You have to put them into the bankroll to earn profit from staking. And then you risk losing coins to winning players.
The rewards from staking almost always outweigh the losses to lucky players, but there is a chance you'll lose some CLAMs.
It means we only risk losing coins to lucky players, but won't gaining coins from unlucky players?
No. You also gain coins when players lose.
Is it possible you give us an option for staking only, or allow us putting for example 90% for staking and 10% for bankroll?
Yes. If you want to stake only you can run your own local wallet. Then you avoid the commission fee as well.