The general perception of wetsuits is “I can hire one at the dive centre” this is true, however depending on where you go dive centres may have a limited range of suits that may not fit your size. If a wetsuit is too tight, it may restrict your movement and you will have an increased risk of cramp. If the wetsuit is too loose, water will pool and it will be less effective at keeping you warm. When you buy your own it will be your desired fit and suitable thickness for your diving ensuring comfort and enjoyment.
From a health and hygiene stand point it is worth considering that rental wetsuits will have been worn by many people and in some cases may even have been urinated in.