If you are not willing to spend hundreds of repair dollars when you get into an accident  or a few thousand dollars when your scooter or motorbike gets stolen, yes you do. Personally I never rent a scooter or motorbike in Phuket that does not at least covers theft as it does occur in Phuket, just like anywhere else in the world.  Cheap Motorbike Rental companies in Phuket  will tell you it never happens but when you ask what they expect from you when your bike gets stolen you will hear that it is you who needs to pay for the bike when it gets stolen. If you rent an Nmax or Honda PCX you are looking at a USD 3000 billand there is little to no chance of getting out of it!