Most are saying that if you hold big amount BTC you choose paper wallet. what is the reason behind that? and just want to know if i keep small amount BTC on paper wallet , what is the disadvantage?
I wouldn't say that most people are saying to keep Bitcoin in paper wallets, especially not in last few years, since hardware wallets became more popular.
Paper wallets are usually limited to only one receiving address, and I recently saw scammers using this to trick people in Australia, so even police was warning citizens.
It's still fine to use paper wallet if you have your own printer, but for small amount of Bitcoin just use regular open source wallets, or combination with hardware wallets and signing devices.