Ok, well, this may be common knowledge, but I couldn't find anything that explained it on the forums, so I went and figured it out myself.
As you know, it takes XP to level up your Heroes, and each single XP can be assigned to a specific Attribute. The question is, for a given level of Hero, how many more XP will I need to reach a desired level? Sure, in your Hero screen it shows how many XP you have accumulated versus how many you need for the next level, but what if you want to know how many you need for the next three or four levels? This can help you plan activities for that Hero so you can level it up faster.
While the numbers initially seem random, it turns out it's a simple formula: Current Level squared times 100. So, to go from Level 1 to Level 2, it takes 100XP; from Level 2 to 3 is 400 XP, and so on. If your Hero is Level 7, you will need 4900 XP to go to Level 8 (7*7*100).
I suppose this isn't very important information, but someone might find it useful. Personally, I use it to calculate which Hero to send on plundering missions, knowing that a given level of NPC gives a specific XP (for example, a full Lv4 NPC gives you 41,770XP).