cy, Stingray, underdog -- thanks for your kind words.
Patents are sought for a very wide range of reasons by individuals and both small and large companies. Some apparently seek patents as validation of their own creativity, etc. For some companies, a patent portfolio reprents an asset that they can point to, to add value to the company. A patent portfolio might be used by a small company in the belief that it provides protection against larger companies who have patents and might accuse them of infringement -- the smaller company can in response to an infringememt claim point to its own patents and offer a cross license. Large companies maintain portfolios for the same reasons. This does not, however, provide much protection against infringement claims from patent holders who do not themselves manufacture or are not otherwise susceptible of infringement claims themselves.
Patents cost money not only to prosecute, but also to enforce. An action in a Federal District court can cost millions of dollars for each side of an infringement action. There is also a potential for an expensive appeal -- because the rate of claim constructions being overturned is so high, some believe that if you lose in the district court on a claim construction, you almost have a new clear shot in the Federal Circuit to get the District Court overturned on appeal.
Part of this belief may be because claim construction is "a matter of law". Normally, the appellate court must pay great deference to the findings of fact a jury in a District Court, but because claim construction is not a fact issue for the jury (the district court judge interprets thew claims) the District Court findingson vlaim construction are generally afforded nodeference and the claim construction issues are decided "de novo" by the Federal Circuit. This, some belive, provides a second bite at the apple of claim construction, with what they believe is a very high, reportedly around 40 percent, chance of reversing what was found below.
The pressures on each side in a patent action in the Federa Courts can be very high, particularly if both sides are manufacturers. For both sides there is the cost of litigation. Attorneys can cost $600 per hour and few patent cases do not have a team of attorneys working on them. Patent cases often involve large numbers of documents, lab notebooks, catalogs, accointing records, meeting minutes, and a whole lot more are potentially discoverable. There are often a relatively large number of witnesses including, in most cases, at least two expert wotnesses *infringement and damages) who themselves may cost as much as the attorney or more (damages experts, for example, often have a stable of their own assistants who review and digest the reams of damages related documents). Each expert must according to the Federal Rules produce an expert report which can be another source of cost. Witnesses must have their depositions taken, sometimes far away from the location of the court. Many of the most reputable patent litigators are located in major cities -- New York, Chicago, San Franciso/Palo Alto, etc. -- and "local counsel" must often be hired as well as regular litigation counsel (the rules of most, if not all, Federal District Courts require the involvement of an attorney admitted to practice in that court's district -- cocounsel admitted in other Federal Districts may the be moved "pro haec" to practice for limited purposes in the district). Patent actions often take longer than most other actions (there are exceptions -- the "Rocket Docket" in the Eastern District of Virginia, the Northern District of California's rules expediting patent actions filed there, proceedings in the International Trade Commision Court, etc.) and it is not unheard of for patent cases to take 5 years to get to verdict. It is also not unheard of (although unusual) for certain types of actions to have budgets in excess of $5 million per year. So the process can be expensive and time consuming.
Moreover, patent lawsuits can be disruptive to businesses. If for example, your R&D department is comprised of just a few indivuduals and these people were involved in the patent application process, as coinventors, etc., then you can expect that they will have to spend siginficant time finding documents, being prepared for and providing deposition (and perhaps trial) testimony, and perhaps have their honesty and/or integrity put into question be opposing counsel. Management faces similar issues and face devoting time to making decisions regarding the litigation and worrying about those decisions. This can divert the company from gmaintaining or rowing a business normally. And they have a significant asset at stake, the patent, which could be found invalid or unenforceable.
For the accused infringer, many of the pressures are the same, except that they face the potential for large monetary damages and, if the patent term has not expired, an injuction preventing them from making, using, selling, or offering for sale the infringing devices. If the product is cor to the companies business, this can truly be a bet the company proposition.
Small companies may not have the resources to participate on either side of a litigation. A larger company with the resources may have the advantage of being able to pursue such an action. This can happen on either side as patent holder or as potential infringer. As it can be in other aspects of business, it can be an advantage to have large amounts of assets to devote to patent issues.