Simply put - the more EXP you earn, the more you can spend on researching (unlocking) the vehicles and modules in the tech trees, and the faster you gain access to the biggest and meanest tanks the game has to offer.
You no doubt understand that EXP is earned through participating and doing well in battles, but there's sure to be some confusion over the different EXP types shown in the game. Why are there two EXP currencies shown in the garage, and what's their relation to each other?
Here's a screenshot of the Detailed Report in the Battle Results screen, which you'll get whenever a battle you were in concludes. As you can see on the bottom right corner, there are two star-shaped icons, with different numbers for each.
That silver star icon, highlighted in the red box, is your Standard EXP.
As a rule, Standard EXP will always stay with the vehicle it was earned with (barring an exception, which will be discussed later). Therefore, the Standard EXP accumulated in a vehicle can only be spent on researching the modules relevant to that vehicle, or on researching higher-tier vehicles that are connected to that vehicle in the tech tree.
In this example screenshot, the Standard EXP stored in this III M7 Priest can only be used for researching the last track module upgrade. The only other module available for research is the engines, but as that costs 5,100 , it's not posible just yet.
There's also another orange star icon represented in the Battle Results page (highlighted in red above). This denotes the Free EXP that you've earned in battle, and is arguably the more precious resource.
Here's why: Any amount of Free EXP that you own is usable in any module or vehicle, in any tech tree.
Like most valuable resources, Free EXP is therefore given out in much smaller amounts after each battle. But that's not the only way to get them...
Here's an example of a vehicle with all of its modules researched, along with the vehicle in the next tier. There's nothing more one can do with Standard EXP here.
When this happens, the vehicle in question is considered an 'Elite' vehicle. It can still be used in battles, but from this point onwards, it no longer produces Standard EXP, but Elite EXP instead.
By itself, Elite EXP can't be used for anything. In fact, there's only one function for it, which is to be converted into Free EXP.
This is where players can convert all Elite EXP earned across all vehicles in their garage to Free EXP at once. A Gold fee is required depending on the amount you wish converted, but as you can see, that amount of Free EXP available to spend on anything you wish is incredibly powerful.