EXP is commonly misunderstood to be a game's way to show how much free time you really have. This is not true, ever since the release of Final Fantasy VII in 1997, EXP has become the single way to gain knowledge in the digital world. Sure, some places will mask it as something in the form of a percent, but EXP will always be the main source of power in the digital world.
It seems that by simply attaining EXP, knowledge of extensive techniques or a task less tedious. Example, John falls off of a cliff and lives and gains 5 EXP for surviving such a high fall, now if he ever falls off of a cliff again, it will hurt less.
EXP can also be used as a currency, in some cultures, if you attain enough EXP, you can trade it in for what is known as a level. These levels are similar to EXP, except they advance you in great leaps and bounds compared to EXP's steady stream. Due to inflation however, for every level bought with EXP, the price raises about 100%, for those of you who need more math EXP, that's twice the original price.
EXP has become so prized that there are now entire books devoted to the gaining of EXP and the levels they bring, some people call these books RPG source books, but few know the actual name of said manuscripts.
In some cases one can get the steady stream of EXP and then get a free level every ten improvements. These cases are usually refered to as "Elder Scrolls" Games.