Is it necessary to buy Rental Car Insurance even though i have my car insurance policy with me

When u rent a car, u have to have full coverage on the care that u own (your personal vehicle) & then that will automatically carry over to the rental. If u do not have full coverage u can add it to ur existing policy for the amount of time u will be renting the car OR just buy the insurance from the rental place. And to answer ur other question, no ur policy will not cover somebody else is car just because you're driving it. Insurance covers vehicles, NOT people, even if u were in an at fault accident, ur friend/relative is insurance would have to cover that loss.

Your policy only covers ur vehicle & the the drivers of said vehicle. Other specified drivers can be named on ur policy (like a spouse, parent, room mate etc..). The insurance does not carry over to other vehicles unless u include another vehicle on ur policy (second car, child is car). You will pay for coverage on each vehicle that u have designated to the policy.
If u r looking to rent a car for travel purposes, the lease will include a charge for for the insurance coverage of the vehicle that you're renting. Companies like Hertz, have deals with insurance companies to pay a flat rate for their rental cars. The amount of coverage that u will pay depends on the amount of travel or time of lease. Again, this surcharge will be included in ur rental fee.
If u drive someone else' car & have an accident, the insurance of the owner or policy holder of that vehicle will have to cover the damage. Again be careful, because while a few states offer policies in which any driver of a vehicle is coverered, most states require u to list the names of drivers on ur policy. If a listed person has a lot of violations or is a high-risk driver, having them on ur policy will cost u more.

* It is true that in states that do not require auto insurance, u r free to opt out of the insurance offered by the leasing company; however, if anything happens to the vehicle, u r financially liable. If you're spending the money to lease a vehicle, then the extra $10-20 daily coverage is certainly worth the expense & will save u the hassle of taking out year long rental coverage with ur own insurance co. After all, how many times throughtout the year do u find yourself renting a vehicle?

you do not need rental car insurance. you can take it, but for the most part, its just another way for the car rental firm to make more money. if you do not take the rental insurance and you do have an accident, the claim will be filed your car is insurance.

if you are driving someone else is car and have an accident, it may not be covered since you are not an insured driver under that vehicle

Ok. You have asked 2 different coverage questions here.
Let me answer the first one. No u do not need to purchase the car rentals insurance. They will tell u that u need there rider insurance as ur insurance company will not pay for the cars rental while the car is being fixed. That is bunk. You have a deductable regardless if u r the guilty party. If u r hit by someone else then there insurance company pays the rental fee loss.
Now for question number 2 if u r driving another person car u will need to look up on ur auto insurance policy to see if u r cover or ask the agent.
(please see ur coverage for all above)

No, u do not need the insurance a rental company tries to sell you. Just understand that if something happens to the rental, u (your insurance) r responsible. This means paying ur whatever ur insurance deductible is.

But since CDW (collision damage waiver) is about $20/day on top of the rental rate, if u rent a car for ten days, you're out $200. If u have a $500 deductible, did u save that much? No.

It is profit for the rental company if u do not use it, possible profit for u if u do ding up the rental.

You r covered in any car u drive, by ur insurance. Check ur policy & state laws.

yes by all means buy the insurance. they can sue you.. that insurance covers you for collision and libality. the extra price is worth it .. if you damage that car or someone lets say scratches it or puts a dent in the door you are liable.. when you rented the car with all that paper work you AGREED TO PAY FOR DAMAGES.. ok buy it..