Lol when I bought my Good Dinosaur pack I hadn't discovered the roar feature, and must have tried every other button because I was thinking they should have one. Can't tell you how relieved and excited I was when I found out from reading comments on this forum that they in fact did have roars lol.
They should implement that extra feature more into mounts/vehicles. For instance I love how Slave I has the missiles/seismic charge combo, but I think it should have had the laser cannon (https://www.youtube.com/watch?v=0kjDg_3qw2w) as the main weapon, and had the seismic charges set to one of the extra buttons similar to the roar.