The significance of recording and storing the DNA of felons depends, to a degree, on who you ask. The answer you get from most people will be that it has major significance, but they may differ in whether it should be seen as a positive or a negative.
As you likely know, DNA can be used to identify the presence of an individual at a crime scene. It can't say exactly when the person was there by itself, or what that person was doing, but when put together with other evidence DNA can be a powerful forensic tool. The trick comes when law enforcement agencies find DNA at crime scenes that they don't know who it came from, such as the scene of a murder in which there is no suspect. Unless you tested the DNA sample against the whole world, you'd have no way of figuring out who that random person was.
The idea about DNA collection is that if someone's committed a crime before, then their more likely to so again, so why not take a sample of DNA at the time their first imprisoned? That way, if we find random DNA, we could search a database to see if anyone who'd been jailed previously was responsible. It's kind of like having a person's fingerprints on file.
Proponents say that it is a reasonable precaution to take, and that by being previous felons, the government has a right to collect this information and store it. These advocates believe it is a "common sense" approach increases the police department's ability to find suspects and helps ensure convictions. The process is painless, and like fingerprints, convicted felons have given up the right to keep this type of "personal property" private.
Opponents would say that this is a violation of a person's right to be free from illegal search and seizure. If the DNA evidence wasn't needed regarding the crime I already committed, it shouldn't be collected against crimes I haven't even committed yet. They'd argue that this is an intrusion on the part of the government, a way to track individuals and the first step toward universal DNA collection at birth. It's also expensive and storage methods prone to corruption.
Whichever way you look at it, the significance of storing the DNA of felons is major. The question is whether it is ethical, legal, or practical.