Remember that a patent requires you to disclose a method. Companies can also keep a technique as a trade secret. Depends on how easy it is to discover. 18 months after you file a patent the patent is public and you will often have no patent issued for several years, so you are telling the world and have no protection. When you do get the patent you need deep pockets if you are going to assert that someone is infringing. Hard for a startup to take money out of product development. That's all my ration comments.
Now to irrational -- VCs want you to check the box that you have patents. But they don't really understand what is protectable and not. So you need to be able to claim you have protection even when everyone hardly knows what you mean. This means in practical terms you need to file something.
Back to rational -- from my experience writing a lot of patents and having 22 patents issued. It's not just one patent but a collection of patents to create a "picket fence" around your primary invention to keep people away from the general area.
