We have always used them and find them absolutely essential to the way our family likes to vacation at Disney. That said, I don't think they are for everyone and may be a waste of money depending on the type of trip you are planning.
If you have not done other Disney trips, two considerations that may sway you one way or the other would be:
1. Where are you staying? Ex. If you're staying in the Epcot resort area, you may be more likely to use the park hopper to go to Epcot or Hollywood Studios multiple times during your trip since they are just a quick walk or boat ride away.
2. How much advance planning are you doing? If you're booking dining reservations, lightning lanes, etc and are going to have all your days planned out, you're probably less likely to have the "free time" to park hop randomly on a whim.