I almost always use a cable release while shooting. This allows me to capture pictures without touching the camera--therefore minimizing the risk of introducing camera shake. Of course, there are other ways to minimize that risk, such as activating a shutter and exposure delay.
But, there is no substitute for the cable release when it comes to very long exposures--more than 30 seconds. Once the shutter speed exceeds 30 seconds, it can't be selected in camera. Rather, the shutter speed must then be set to Bulb and triggered by pressing the shutter and holding it down until the exposure ends. The cable release allows you to press the shutter without touching the camera...then lock the shutter down through the mechanism on the release.
Years ago, I got burned when my cable release malfunctioned during a trip. I was quite far from the nearest city with a camera store--Moab, Utah. I headed right to the camera store when I arrived in Moab to buy the cable release. The sign on the door indicated that they were closed for the season and would reopen four months later in April! A man from a nearby general repair store said that he could perhaps try to repair the cable. The issue was that the labor would far exceed the $5 that I paid for that third party release!
Since then, I bought the genuine Nikon MC-30 cable release. It's more durable.
Not wanting to chance it, I brought a backup cable release (one of my leftover third party cheap ones) with me on this latest 32 day road trip as well.
My Nikon MC-30 served me well for nearly three years. But, three weeks into my trip it failed! Fortunately, I had the foresight to bring a backup. Unfortunately, the backup was dead right out of the box! Once again, I was without a cable release. And, I had some long exposure photo shoots on my itinerary.
The next day, I visited Samy's Camera store in Santa Barbara. They had a suitable cable release. It was a third party brand and they charged me $35--seven times what I would pay for a comparable one on eBay. I asked the sales person if he thought the release would hold up for the next two weeks until I got home. He said it it certainly should.
Naturally, I treated this third cable release with kid gloves. I was careful to never stress the cord. When activating the shutter, I made sure to press it down softly. With one day left on the trip, the cable stopped working!
Now that I'm home, I ordered another Nikon MC-30. Actually, it's a new and improved model...the MC-30A. Let's hope it lasts as long as my MC-30 did!