If you are referring to the "rested" exp bonus, then I can help you out. Basically, anytime you log out in a sanctuary (camp around an aetheryte crystal) or in an inn room, you'll received a bonus to any experience you earn depending on how long you stay logged out. It is most beneficial to the player looking to level up for them to log out in a sanctuary EVERY time they log out. In 1.0, IIRC, you got 50% more experience for each action that rewarded experience(not including quest rewards). The bonus applies to all classes/jobs. This means you can use half of the bonus to help push you to the next level on lancer and then switch to botanist and use the last half to help you level botany up. The bonus appeared as a highlighted area on the experience bar. It was like a green highlighted area. If it ended up pushing you to the next level, it would highlight the entire exp bar as a pinkish red color and then once you leveled up, it would change to a green highlighted area to show when the bonus would stop.
I've never heard of a special exp bonus that starts to apply for people just for getting a class to level 50. I don't think this is accurate. If this was found during an explanation of how people would level up after they get their initial lvl 50, then this is one thing that would help boost them up. It will certainly be possible to use while leveling up your first profession. This also does not include any bonus that housing adds. I'm not exactly sure if the rested bonus and the housing bonus will stack or how it will work at all. It may only work for experience gained while in the house. I think it was mostly intended to help people level up their crafts.