Having a single stream of income is always a terrible idea.
If you rely solely on your YouTube ventures, the moment it goes FUBAR, you'll have no income.
If you rely solely on your office job, the moment you get fired, you'll have no income.
But if you have both, if one of those went FUBAR, then you atleast have the other to support you. One may provide you less significantly than the other but its a million times better than nothing.