The natural tenderizing process for sirloin steak as well as many others produces dry aged beef. Usually, the beef whether a sirloin tip roast or not, is aged from two weeks to just over three weeks in a very expensive process. But if you are a fan of dry aged beef, it is definitely worth every penny. And for those that are true lovers of this kind of aging process, they will travel far and wide to find a restaurant that serves this kind of beef. They will also scour the internet to discover the best beef aged with this process that they can find. 

The cut of beef is placed in a temperature that is closely controlled along with the humidity. The moisture in the beef, whether it's a sirloin steak, porterhouse or whatever, is evaporated which concentrates the flavor in the steak. When that happens, the sirloin tip roast or other cut of beef has natural enzymes that break the tissue down and creates a tenderer cut of meat. After the dry aged beef process is over, the butcher now has to trim the crust off the meat that has built up and that is why this smaller piece of meat is more expensive than a normally aged sirloin steak, T-bone or whatever. 

Since dry aged beef has a much stronger flavor than wet aged, many people grow to love it so much that they refuse to eat anything but that. And the longer the meat is aged, the stronger the flavor will be. For example, a sirloin steak that is dry aged for 3 weeks will have a stronger beef flavor than one that is aged for two weeks. The same with sirloin tip roast or any other cut of beef.