Maremma Sheepdogs have a double coat that acts as a winter and summer insulation similar to your home insulation so it would be in the best interest of your dog not to shave your Maremma.
Maremmas can develop some mats in their winter coat, this is normally from weedy seeds.
Your dog can groom these out themselves to a certain degree.
Most mats would normally shed in the summer. What mats that can’t be teased out with you fingers could be cut out with a pair of scissors.