I wouldn't say it's an absolute must but I highly recommend it. Partly, you can't predict the crowds, despite using the crow calendar and if you notice wait times are significantly lower in another park you will want to go. Also, if you go to dhs and it closes at 8, everyone has more wind in their sails, and mk open until 1, you might want to go. Or everyone was too hungry /tired to stay for something you wanted to see that they only do a few times a week, fantasmic, you can head back to the park. So, I would suggest you do it unless it's going to break the bank.