Any large business firm or corporation is going to have a need for a third party company which they contract to destroy their documents. This is just a reality of business in the modern corporate world. First of all, even though there has been a very large move to electronic record keeping of many kinds, the law requires many documents to still be filed in hard copy. Many businesses have literally what amounts to truckloads of paper documentation that they needed to have destroyed on a yearly basis, and it is simply not time or cost effective to have people within their organization taking care of the business of shredding paper when there are contractors with the equipment and the expertise to do the same in a fraction of the time, and therefore cost.
And those are two of the factors you should look for when weighting paper shredding companies. The time it will take them to destroy the volume of goods you have to be shredded, and what it will cost you to have them do that. In many cases, the factor of time will be determined as much by their equipment as anything else. The companies that perform this service typically have large scale industrial shredders which can not only process enormous amounts of paper at a given time, but they also destroy it more completely than a traditionally office paper shredder.
This is another reason why people should consider a company to shred paper for them rather than trying to do it themselves. The law requires corporations to shred and destroy many different kinds of documents, however, it is also legal for people to go through your garbage and examine your shredded documents, which has happened in the past, necessitating the need for shredders that do a more thorough job of destruction, which is the role of your company you contract to do this for you.
The final thing you want to consider is confidentiality. The documents you are destroying are likely being destroyed either because they contain confidential client information which must be destroyed by law, or information which could be used to perform identity theft or corporate espionage against your own company. These are all crucial pieces of information, so you want a company that either has a strong built in confidentiality agreement or is willing to sign one of your own that your lawyers have drawn up for you instead.