Why Patent?
Protect a new product
The most logical reason to patent is that you have come up with a new product idea that you think you can make MONEY from! Technically a patent gives you the right to exclude others from doing what is in your patent (provided you have a thick skin and money for infringement litigation). But you should think of a patent as insurance to allow you to continue to do what you do.
Increase the value of your company
Is that IPO coming up? If you can show that your products are protected by patents, the is no question that the value of your company will increase provided you have a salable product or idea. Sometimes a well written application (or provisional application) can be worth as much or more than an issued patent as you can continue to expand the patent claims with a procedure called a continuation during the patent prosecution process.
Exploit an idea you choose not to develop
If you obtain a patent and can't afford or don't want to develop a product based on it, you can license it to others so they can develop it and you can receive a licensing fee. Alternatively, if someone develops your patented idea without a license agreement from you, you can sue for infringement. If you make a habit of suing infringers on a regular basis for patents you don't intend to develop, then you would be referred to as a non-practicing entity (otherwise known as a patent troll).
Nuisance value
Want to make things difficult for your competitor and cost them money? Get a patent that they can't avoid infringing when they build their product. Have me perform a white space analysis around their patent portfolio and look for holes you can fill.