At the CMU Grappling Club, we practice both gi and no gi grappling. On the days that we practice with a gi, the uniform is required. It is required because techniques are taught that specifically require the gi, such as choking with the lapels and grabbing the jacket. If you are not wearing a gi, you cannot perform these techniques correctly and will not be able to participate fully.
Grappling in the gi will really improve your skill level. It is necessary to wear a gi to compete in many grappling tournaments and in order to train at most Brazilian Jiu-Jitsu schools. Therefore, it is important that you purchase a gi for your grappling training.
Any type of judo or jiu-jitsu gi will be fine for grappling training. Karate gis and other gis made of thinner material will not work because they will tear under the stress of the pulling and throwing techniques we practice in grappling.
If you do not already own a judo or jiu-jitsu gi, you can order one online easily.
When ordering your gi, make sure to account for the shrinkage that will occur when you wash and dry it. It is made of 100% cotton and will shrink significantly during the first few washes. If you are close in between two sizes of the gi, make sure to order the larger size to account for the shrinkage. It is much better to order a gi too large and shrink it to fit than have one that is too small.
Instead of just linking to a specific gi like I've been doing, the link below will take you to a gear and equipment forum for BJJ. Pretty much every type of gi and its advantages/disadvantages are discussed here, so you should be able to find plenty of information and a gi that fits your needs. There are also tons of links to reputable vendors to buy it from.
Again, if you're confused about anything, just email us and we'll help you out.