Because the marketplace for technology is constantly changing, you may not have much time to prove that your machine, process or discovery is "new." Given this fact, it's important to file your application as soon as possible after your invention is complete, since the first person to file a provisional application or a full patent application will more often than not be considered the inventor. Note, too, that for an invention to be eligible for patent protection, a patent application must be filed within one year of (a) putting the patent on the market for sale and public use; (b) disclosing your invention to the public in almost any generally-available form; or (c) filing a Provisional Application for Patent.
The early filing of a patent application has other benefits as well - once the application is published, potential infringers are put on notice that an application is pending. If a patent is granted, the inventor may seek royalty payments from any person who made or used the invention during that pending period.