You probably know someone who already sings the virtues of their mechanical keyboard (or that person may be you). There are several reasons to consider a mechanical model, some of which you may have heard:
Mechanical keyboards can minimize typos. Depending on the type of switches you get (and we'll dive into that later), you not only get specific tactile feedback when you've pressed a key and it's registered on the screen, you'll also never wonder whether or not you've actually tapped a key or not. Once you get familiar with the way the tactile "bump" feels with certain typing-friendly mechanical keyboards, you'll find yourself more sure of the keys you've pressed and not double-typing to make sure you've actually pressed a button. The sound of a mechanical keyboard can reinforce the tactile feedback as well, as opposed to quieter scissor or membrane keyboards, where you may not even know if you've hit the right key in the first place.
You want a keyboard that'll stand the test of time (and use). One of the biggest benefits of mechanical keyboards is that they're durable and meant to stand up against heavy use. Depending on the model you buy, the keys are rated for dozens of millions of keypresses, which is way above and beyond the standard duty expectation of a membrane keyboard. If you're the type of person who wants a good keyboard to stick with you for the long haul, or you notice you're hard on your membrane keyboards, a mechanical could change the way you work. Plus, since the switches are mechanical, the keys pop off and go back on easily—that means a lost key or bent scissor switch doesn't mean a keyboard in the trash can. Cleaning and maintenance are a snap.
Mechanical keyboards are more satisfying to use. This is pretty subjective, but most people who use a mechanical model on a daily basis will tell you that it's just a more satisfying typing experience. The audible key-clicks and the sure knowledge every time you press down on a key that it's registered properly is a feeling you really have to experience to appreciate. Plus, as we mentioned, depending on how you use your computer, that audible and tactile feedback can improve your game or help you minimize typos, especially if you're a fast typer. There's even debate over whether using a mechanical keyboard (or at least some mechanical keyboards specifically) can alleviate the pain of RSI (Repetitive Strain Injury) in heavy users.
You have a strong sense of nostalgia. If you're old enough to remember the IBM Model M keyboard or more recently the Apple Extended Keyboard, you can probably recall how they felt to use, and the sounds they made when you clicked away on them, whether they were your first computers or you used to work on them regularly. Modern mechanical keyboards can bring that sensation back, depending on the switches you buy. We'll get to that in a moment.
These aren't the only reasons, but they're some of the best ones. Not everyone is going to love a mechanical keyboard. Some people will find them too heavy, too clunky, too loud, or just outright annoying compared to slimmer, quieter scissor switches or membrane keyboards. They're often a bit more expensive than traiditional keyboards as well, esepcially if you're the type who's comfortable using whatever keyboard came with your PC or you picked up for $5 at your local department store. If you're an enthusiast however, do yourself a favor and give one a try, if not at home then in a computer or electronics store like a Fry's or Micro Center. You'll immediately feel the difference, and you'll want to take one home with you.