Hops are flowers that are used to add flavor, aroma, clarity and shelf life to beer. These qualities are present in all hops, but not in the same magnitude. Some hops are very well suited for bittering a beer, but might not have the best aromatic properties, and vice versa. Some hops are well suited to impart different flavors to beer besides bitterness, and can add citrus, floral, piney, grassy, spicy, etc. flavors. Meanwhile some hops are well balanced, and are usable to add many different characteristics. Because of all of these variants, there is an ever expanding selection of hops being genetically engineered to provide aroma/flavor/bitterness combinations that are the most desirable.
"Triple Hops Brewed" is now a common term thrown out by Miller Lite to explain how they get their "Great Pilsner Taste", and even though I disagree with them on their taste they are touching on a fundamental aspect of adding hops to beer. Don't tell Miller, but depending on the style most homebrewers add hops to their wort at least three to four times. This is because different characteristics can be created or destroyed within the beer depending on how long the hops are in the wort, and the temperatures that they are subjected to.
The bittering of the wort is the easiest characteristic to extract from hops, but it takes the most amount of time. When the wort is being boiled 60+ minutes this bittering aspect is the reason. Resins within the hop flower aren't very soluble, and require boiling to isomerize in the wort. These resins contain alpha and beta acids that are responsible for bittering the beer. Alpha acids are the stars of the show, because they are usable when the hop flower is fresh. The percentage of alpha acids compared to the weight of the hop flower will be given to a brewer by the hop supplier, and will indicate how much bittering "bang for your buck" that that hop will provide.
These hops that have been in the boil for 60+ minutes have added bitterness to the beer, but most of the other characteristics that the hop could have provided have already boiled off at that point. That is because these flavors and aromas are located in oils within the hop flowers. Heating these oils will cause them to boil away with steam vapors. This is why hops will be added during the last 45 or 30 minutes of the boil for flavoring, and 15, 10 or 5 minutes of the boil, or during the whirlpool or secondary fermentation stages for aroma.
All of these hop additions would add bitterness, flavor and aroma in different amounts depending on the type of hop used, and the length of time that it is in the boil. It is standard practice to use the bittering characteristics of a high alpha acid hop during the beginning of the boil, and hops that are known for their flavoring and aromatic properties later. Don't limit yourself to this notion of "Triple Hops Brewed", because there are many different times that hops can be added to wort, and they will each add different complexities to your beer.
