This post is one of ten appearing in the series 10 Ways To Improve Your Landscape Photography. I remember thinking tripods were useful but too heavy and inconvenient to use so I'd leave it at home. My images seemed sharp enough anyway (in retrospect, they weren't). I use my tripod all of the time and I think it's a vital piece of equipment for a number of reasons:
Longer Shutter Speeds
The obvious and main reason you need a tripod is for longer shutter speeds. If you're shooting at Golden Hour there is less light around and you can find yourself shooting at up to and over 1 second, which is far from optimal for hand holding. So for the sharpest images you really need to be using a tripod.
If you're looking to blur the motion of water, clouds or anything else moving in the landscape then you're looking at several seconds perhaps even minutes which really isn't viable without a tripod.
Tripods slow you down. You might think this is a bad thing but it's a real plus. It makes you consider your shot more carefully and the compostion you want. If I "can't be bothered" to set-up the tripod then I have to ask myself why I'm taking the shot at all.
You can make small, well considered adjustments to your composition. It's normally pretty uncomfortable holding the camera to your eye for a long period. You become more concerned about getting the shot off than you are at making fine adjustments to your composition or exposure. Having it on the tripod gives you the time to deliberate on your decisions.
Waiting for the Moment
You're unlikely to hunch with the camera to your eye waiting for that wave, cloud or beam of light to be in the right spot. You're just going to squeeze the trigger. Having the camera on the tripod let's you have it all set-up and you can watch the scene for the right moment.
Whilst certainly possible, it can be tricky to use filters whilst handholding. A full ND will give you longer shutter speeds and it's tricky getting the placement right on an ND grad whilst holding the camera in the other hand.
Tripods may weigh a lot and slow you down but the benefits far outweigh the negatives for a landscape photographer.