I remember thinking I didn't need one and then started using one at a quilt retreat. I couldn't believe the different perspective I got on my work!
Mine is a foam wallboard that a construction friend got for me. I used a glue gun and a 1/2 bolt of cheap flannel to cover it. I'm blessed enough to use my finished basement as a sewing room, so I can 'see' my work in progress. It's been a big help.
But, JIC you don't have the room...when I teach at the store where I work, when it's time to preview our blocks, I just bring in a large flannel-backed vinyl tablecloth - pin it to the wall & voila! that works too.
Don't go without one!