Holding onto things unnecessarily could be disastrous; best habit is surely to let go. Holding onto things can make you physically, spirituality or mentally uncomfortable. Let me relate to a particular exam I wanted to write; I made a mistake to memorise almost everything I read. It led to confusion, making it difficult to make sense of what I read. To solve the problem, I "let go" the burden I created in my brain and my brain worked normally again. If you want to make progress in life, you must cultivate the habit of "let go".