This post is written from the perspective of a UK-based European Patent Attorney.
1. The value of a patent is of course very much related to the scope of its claims and the extent to which they cover commercially important subject matter. Therefore when pursuing patent protection applicants normally have the strategy of obtaining the broadest claims, and most would have the view that there is little downside to having claims which are too broad.
2. The claim scope that is granted will be a balance between the degree of extrapolation possible from the experimental work and the prior art available to the Examiner. With the limited resources available to an Examiner, in comparison say to a Court, it is easy for overly-broad claims to be granted.
3. Normally pursuing broader claims will entail using more complex arguments and there is the likelihood of more examination reports issuing. In the case of European applications Oral Proceedings are also more likely. Therefore there is likely to be increased cost for an applicant.
4. Broader claims are less likely to be valid, and thus there may be problems with enforcing them. However there will normally be the possible of amending claims in post-grant proceedings which should make it possible to enforce the patent.
5. Broad claims are a feature of certain technology areas, particularly in biotech where the underlying concept for the invention can be very broad. In such areas applicants have little choice but to pursue broad claims to adequately protect their inventions.
6. Not all applicants wish to pursue broad claims, and so patent attorneys need to tailor their advice accordingly. Some companies will only want to protect their particular activity or product and see little point in pursuing broader claims. The company culture may see patents as serving this narrow purpose, and such a culture may not be easy to change.
7. If one pursues broad claims then prosecution of the case in different territories becomes more complicated. It is more likely that different scopes of claim will be granted in different countries, and therefore different arguments would be used for defending validity. That means a single uniform strategy for prosecution of the case cannot be used.
8. Having broader claims may cause third parties to take action against the patent. In the case of a European patent parties may be more likely to file an opposition. A company needs to assess whether this is likely when pursuing broad claims, and whether the commercial worth of broad claims justifies defending them against attack by third parties.
9. Where the claims of a patent cover more than what the company is itself doing there is the option of giving licences for other technologies covered by the patent. However many companies are not geared up to do this, and thus will never fully exploit the broad claims of their patents.
10. For the sake of completeness patent monetisation entities should be mentioned which provide an alternative way of exploiting claim scope which a company cannot do itself. However this is clearly a controversial option.
You may also wish to see related articles Top 10 Uncertainties in Patents and Top 10 Tips of Getting Difficult Patent Cases Through.