Small investment means smaller ROI. It will take you a long time before you can get a profit, so it's a little waste of time. Even if you put all the interest from your investment, if it is small, it won't matter.
If you are going to invest, I would suggest that you think of the ROI like atleast half of your daily salary from where you are working, otherwise, it's a waste of time and I think if you are investing in a wrong place, then before you can withdraw, they are gone.
Just priority first all the important stuff and savings would be divided for investment.Dont risk too much because you will surely feel the effects ones those investments do failed down.