Inversions are great for body balance, concentration and circulation as well as increasing core strength. Although we work with our shoulders and arms in these postures the whole body must be active to help us move the energy from the ground and up.
The inverted postures reintroduces us to our inner child and allows us to be playful, light hearted and may also build up our confidence. In the summer one should be careful while practicing inversions as Sirsasana (headstand) and Adho Mukha Vrkasana (handstand) as they tend to create more heat. Inversions of the cooling type are Sarvangasana (shoulderstand) and Viparita Karani (legs up the wall pose).
The essence when you practice yoga is to know your body and not to perform any poses which are beyond your abilities. Allow yourself to be playful but always be conscious!
Remember not to practice inverted postures during the menstruation as they arrest the natural menstrual flow.