Not an indicator, it just happens that it may be a good indicator for some assets for some time. Bitcoin is a currency and hopefully you will engage yourself appreciating that it's widely use as a medium of exchange. It is for long term, you do not have to tune up for its movement every single day and rant here because it is given that it is volatile.
Whenever the bitcoin market is up it can help to decide whether some altcoins can have a good performance too. Whenever the price of bitcoin dump altcoins somehow affected too. So in investing or trading we must know the risk and decide whether we gonna invest in long terms or were onto day trading. This method bot requires skills and patiemce to know the market status and where it can possibly upto.