Patent attorneys often attempt to get the broadest possible coverage for a client's invention because that can usually make the patent quite lucrative. Patenting broad claims can be expensive during the patent procurement process because patent examiners are reluctant to let broad claims issue and so there may be multiple back-and-forth communications between the patent examiners and patent attorneys. However, patents with overbroad claims can be expensive to keep enforceable, e.g., when a third party requests the U.S. Patent & Trademark Office (USPTO) to reexamine an issued patent in view of prior art.
For example, the Electronic Frontier Foundation (EFF) has apparently requested the USPTO to reexamine U.S. Patent No. 7,568,213. According to the EFF, this patent is purportedly directed to "podcasting." When a patent is under reexamination, the patent holder must expend resources (e.g., patent attorney fees) to work with the USPTO to define the appropriate scope of the patent's claims in view of the newly identified asserted prior art.
During prosecution, patent attorneys, inventors, and anyone involved in a patent application have a duty to cite all pertinent prior art they are aware of. However, it is nearly impossible in most fields of human endeavor for the patent attorney, patent examiner, or even the inventor to be aware of all pertinent prior art. Thus, it is quite easy for overbroad patent claims to issue. Sometimes, the best prior art is not even found until the patent is asserted in an infringement lawsuit because the alleged infringer is motivated to prove that it is not infringing a valid patent.
Thus, smart patent attorneys attempt to patent claims of varying scope -- from broadly encompassing the subject matter of the invention without crossing into the known prior art down to narrowly encompassing a specific implementation that is reflective of the client's commercializable product.