Today, with so much information available and the ease of storing and retrieving information, many employers keep vast records of their employees - even when they are first hired. Some of this information is important to the job at hand and will be needed in the future. Some information is just for emergencies, such as emergency contact info. Other facts might help the employer plan the schedule, like if you are married and if you have kids. However I think that a lot of the information is unrelated to the hiring process and really none of the employer's business.
Henry Ford, founder of Ford Motor Company, hired many workers during his life. So it is certain that he knew a thing or two about the hiring process. But in contrast to a lot of the ways that most employers do things, he did not care about anything other than the job at hand. Therefore he only kept a small amount of information on the men he would hire. Ford wrote in his book My Life and Work, that "In hiring a man the only data taken concerns his name, his address, his age, whether he is married or single, the number of his dependents, whether he has ever worked for the Ford Motor Company, and the condition of his sight and his hearing. No questions are asked concerning what the man has previously done."
This might be shocking to some. Most employers are so hung up on people's past performance and education - whether they went to a good school, if they graduated, what degree they got, what their major was, how many jobs has he had, how long was he at said jobs, is there any gaps in his job history, has he ever been in trouble with the law and if so what for, and on and on. Yes it might help you find a good employee. But it might also help to weed out a great employee just because he doesn't look perfect on paper. The great employee might be overlooked for a merely mediocre one just because one person's parents had money to send him to a better school or a person wasn't able leave the state to attend a better university. There are many reasons that you might be overlooked in an interview, but the only real way to know if a person will be good for the job is for them to actually do it. At the very least, ask questions and pose scenarios that might come up at the job to the candidate. When evaluating prospective workers, I don't care about their education or past work history. All I care about is the job at hand. So if I am hiring a writer, I may want to see his past writings. If hiring an artist, I may want to see her past artwork. But many jobs can't be judged in this fashion, so it can be really tough to determine who to hire. I know this so I can see why some employers want to have a way to judge people and determine who is the best candidate. But really there is no perfect way. Some people might get nervous and not do well in an interview, but that doesn't mean they aren't qualified. Just because a person is good with people and quick on their feet doesn't make them fit for the position either. So really there is no perfect way to determine the best person for the job. Some jobs require more information than others, but don't ever judge people solely on what it says on their resume. Don't just hire somebody because they went to your Alma mater. Also don't pass somebody up because they didn't go to school or they got an unrelated degree. You never know what people are good at and how they might perform at a job unless you give them a chance. It might take longer to weed out people if you give a few people the chance to try their hand at it for a few weeks each, but in the end you will find the best fit for you and your company.