i didnt take it but my two friends did all 3.
i think if you are passionate about science and plan to do it in the future, you will be fine. each of the three sciences are quite different - bio is all memorisation, physics is (arguably?) mostly analytical, and chem lies somewhere in between. and they all work together pretty nicely -> bio and chem content often go well together, as does chem and physics.
one of my friends who did triple sciences only did 10 units (only other subjects were math and english), whereas my second friend who did this did 12 (science + math ext). both of them liked it and hence chose to really focus on sciences. if you are passionate at this level it should be ok.
on another note, i was gonna take all 3 sciences but decided against it since i felt that it would be too much of one subject type - decided to switch physics out with history and was much happier! so this is another factor to consider, whether or not you would get burnt out of science cause u would be studying it nonstop.