I think this forum has lot of regular gambler so I am interested to know how much they ever spend as highest bet amount in very single bet.
I have seen people placing crazy amount of bet size at crypto-games.net. I have seen people betting like 15 BTC with maximum win chance. I know that is crazy but it is true. Just letting you know, each casino restricts the maximum bet size. Usually, it is restricted based on the bankroll of the casino (usually max win is like 10% of the bankroll) or else people would empty out the house in just 1 single bet.
Risking 15 BTC in a single bet is just insane. When you are not sure that you will win then how can you spent this much big amount in just one time bet.
You should spend small amounts in betting because in this way if you lose then only a small amount of your money will be lost and you still have many more money to play and recover your losses.
It sounds insane for us who do not even have that amount of money, but 15btc could be something really small for whales. Regarding max bet size, usually there is max profit per bet only not max bet amount and AFAIK the max profit per bet is 1% of the site's bankroll. I have never seen any sites letting their players to win 10% of the bankroll on a single as it will be very dangerous for the bankroll.
Overall, small or big bet amount depends on the gamblers. I do believe gamblers have their own limit to bet.