You should always go into a patent program with a clear objective in mind.  In some cases, the costs and hurdles of patent protection outweigh the benefits.

For example, if your invention relates to a method of manufacture that cannot be discerned from the final product, you may wish to keep the invention as a trade secret rather than disclose the invention and limit your ability to maintain a competitive edge to the 20-year patent term, bearing in mind that as soon as a trade secret is used, the likelihood that the secret will be leaked increases exponentially.

If your invention can be easily discerned from the final product and easily replicated, such as a novelty item or produce, the exclusive rights obtained by a patent may be of questionable value given the extremely high costs of litigation to enforce them, especially if the infringers can pop up and disappear overnight. It may be more useful to take the funds that would otherwise be spent on patent filings to develop a competitive advantage based on marketing or other factors.

Clearly, if there is lots of prior art around, the scope of monopoly that you might be able to obtain may be very narrow, with the result that a competitor may be able to come pretty close to your invention without infringing your patent. You can sometimes get an estimate of how broad the claims of your patent may be by retaining a patent agent to conduct a patent search and opinion. This may help you decide whether or not to invest in the costs associated with drafting and filing a patent application.