Most first time visitors to Vegas, flying in to McCarren Airport, get to their hotel via cab or hotel shuttle. Likewise, getting around town is easy by cab, and it can be fun, although it can get expensive. A cab ride from the airport to most hotels is at least $20. depending on the distance. In fact, you can figure a minimum of $20. for a cab ride just about anywhere. If you take a cab to the Fashion Show Mall, or for a couple of evenings out, your total cab tab for the whole trip can easily be $200.+
After you've been to Las Vegas a few times, however, you might want to do some exploring around town (and maybe out of town), and the best way to do this is to rent a car. I always rent a car when in Vegas, so I can go where I want, when I want. Parking is never a problem. All of the hotels, and lot of restaurants and shopping venues have valet parking. And you don't have to be a guest at any hotel to take advantage of the service. It's usually 'free', although a two or three dollar tip when the car is brought back is appropriate. I've never stayed at New York, New York, but one of the first stops I make when visiting Las Vegas is Greenberg's Deli, at NYNY. Rather than parking in their cavernous parking lot and getting lost on the way to the casino, I just drop the car at the valet stand at the main entrance, go get my Reuben sandwich and egg cream, and play a couple of shoes of blackjack on the way back out to the valet pickup area. Minutes later, the car is delivered by a smiling attendant, and I'm on my way.
I usually rent a compact or mid-size car, which costs a total of about $200. for a week, which I pick up at the airport car rental center, which houses all of the rental agencies, and is a couple of miles from the airport. There is a free shuttle bus right outside from the baggage area that takes you there. I usually rent from Thrifty or Budget, which I have found are consistently the best value, and I rent online in advance. (Dollar is also a good deal, but they own Thrifty in Las Vegas, and therefore their rates are identical.) If you sign up for their services online, where they store all of your information, including credit card info, etc., it will save you much time and grief at the rental center. Having reserved your car online, you can proceed right from the airport shuttle to the rental car lot, bypassing the lines of squares at the rental counters, and pick out your car. All the paper work is done in advance, and you just sign it as you drive the car out of the lot.
When renting a car, you are responsible if the car is stolen, or if there is any damage to it while you are renting it, no matter the cause. You can purchase the insurance offered by the car rental company, (usually called 'Collision Damage Waiver' [CDW], or some such), which can cost a minimum of $15./day. This is in addition to the base rental charges, and can easily double the total amount paid for the rental. But many credit and debit cards, especially those used for a business, cover damage to a rental car, as long as the card is used to reserve and pay for the rental. I also have a 'rider' on my personal auto insurance policy that covers any damages or loss to a rental car. It costs me an additional $25. every six months, but is worth it, because I don't have to buy the CDW offered by the rental. It's always a good idea to keep some proof of the insurance with you in the car.
Las Vegas is an easy city to navigate, although there is a lot of fast moving traffic, all the time, so if you are not used to that, it takes a little getting used to.
Drive to to Hoover Dam, or Red Rock Canyon. Most rentals have unlimited mileage, so the only additional cost to driving a lot is the gas (I've rented a car in Las Vegas and driven to Tucson a couple of times; don't ask why.)
Now this is part where I complain about renting a car. Below is my car rental reciept for my last trip.

Many cities levy exorbitant taxes on hotels, cabs, and rental cars. These are typically fees that they wouldn't dare charge their own citizens, but the rational is that they can nick the 'visitors' a little (or a lot) more, and therefore add to the city coffers in a way that is a little less painful to the locals. Las Vegas is no exception. In fact, I have rented cars all over, and I've never seen any city with higher rental car taxes. Witness the following receipt from my last rental there. The base rate is $135. and the total bill is $200. The 'taxes' account for over 32% of the total!
And look at some of the line items. Note that the sales tax is included in $135. 'base rate'. I assume the APTAX is 'Airport Tax', which most cities apply when you pick up a car at the airport (although it's usually a lot less in most other cities), but what the #*$&# is the CFC and all that other stuff?
Oh well, in any case, despite all the fees, it's still less than using cabs, and, a rental car gives you the freedom to go where you want, when you want. Just make sure you're sober.