To answer this question briefly, unless your landlord requires that you carry renters insurance, you don't need it. That being said, we do strongly recommend it; the benefits and low cost may surprise you.
Low Cost - Did you know that most renters' insurance policies are only around $20 - $25 per month? This depends on the coverages of course, however most people can get adequate coverage for this cost.
Protect Your Property - Imagine someone broke into your home and stole your belongings (tv's, computers, game systems, etc. add up fast!) - having personal property coverage on your renters insurance means you would only have to pay your deductible to recover your property. You can also schedule personal property on most renters policies.
Liability - Say someone injures themselves while visiting you, are you aware that you could be found liable for their injuries? What if you start a grease fire while cooking - did you know you could be found liable for the damages that the fire causes? Renters insurance provides personal liability coverage generally between $100,000 and $500,000 that could protect you from paying for damages out of your own pocket.
Multi Policy Discounts - Most people know that packaging your auto and home policies will provide a discount, but renters policies apply in this situation as well. We have seen plenty of times where the discount on an auto policy actually pays for the renters policy (and then some!) of course this may not happen for everybody, it really depends on your auto policy premium since it is a percentage based discount.