When we think about investments we imagine investors with big sums of money, so for btc casino it would be 1 or more btc, for instance. However, the minimum amount you can invest is usually 0.01btc which is only 10$. Do you think such investments are profitable but you earn small sums or maybe they don't make sense at all? Can someone explain it to me?
Yes, small investments can make sense in 2 situations:
1) Investing with leverage
Some casinos allow this option, so for example 0.01 BTC with 10x leverage will have the same profit/loss as 0.1 BTC investment, meaning that you'll see higher profits, but you'll also lose all your investment if casino will lose 10% of its bankroll.
2) Investing in new underfunded casinos
Lets say there's a new casino opened just yesterday and has 0.99 BTC bankroll, you invest 0.01 BTC so your share is now 1%, then someone comes and loses 0.5 BTC, in that case you will get 0.005 BTC profit, which will be a half of your investment. The problem here is that this is very risky, someone could almost just as easily win 0.5 BTC, and you'd suffer 50% loss.
tl;dr you can make a big return from small investment by increasing its risk
All the roads lead to Rome, you can trade with less the 0.1 bitcoin or even by 100 bitcoins and you eventually come to the point when you realize that no matter how much you invest you are risking your money, but as I see it really depends on the person if you have only 0.1 then it is not worth investing and risking all your money, but if you have 100 bitcoins than it won’t bother you losing 0.1 bitcoin.