By absorbing the micro-shocks when rolling over uneven and rough surfaces, especially when you are going at a speed, suspension is good for keeping you comfortable as you scoot. However, there is always a trade-off as a suspension system will make your adult scooter heavier, meaning you do sacrifice a little on both performance and portability. And with the extra moving parts, you do get a noisier ride. So, when deciding whether to go for a model with suspension, you need to think about the main reason you are getting an adult scooter for. For example, if you regularly commute the same route and know it has its rough moments, a scooter for adults with suspension is a good idea as it will make your ride a breeze over rough or uneven surfaces.
But if you are a leisure scooter or your routes vary from smooth to a more bumpy and prefer to have a lightweight, portable scooter, then you could happily go without. If you do opt for no suspension, look for other features that can help to smooth out your ride, such as skateboard-style cambered wood decks rather than rigid aluminum and air-filled pneumatic tires.
Ultimately, it is a personal choice and a few bumps in the road will keep you on your toes!