I agree. If you can only afford small investment at this time, then you should do. But remember that small investment also yield small returns. You just have to learn how to roll your small profit to make another profit out of it. So in no time your profit will run exponentially. So start small but aim big.
This thread is about investing in BTC casino bankrolls, but people here just spam their comments about general investing. So, specifically with investing in BTC casino bankroll, you can't get exponential profit, you can expect 50-60% ROI at best. By making small investment like $10 you'll get only $6 in a year. The only thing that can help you to increase profit is leverage, but only few casinos support this option.