If you do this, then you can cause a lot of undesirable effects. Some channels could disappear whilst others are OK, If you unplug one of the downleads, it affects the other, On analogue TV, it can produce ghosting etc.
With aerials and cables it is important to preserve the impedance match and this is what a proper splitter does. You will get loss no matter how you split the feed but a proper inductive splitter is the best option.
Frank