As you delegate, it cuts down your voting power and your available resource credits that you have for use in your account to do posts, comment, and vote on others' content. If you are down around 1,200 HP, you need a margin to keep growing and engaging personally.

Think of it this way: 700-1000HP is kind of a floor that you should build so you can do everything you want to do and also engage robustly with other users. At 1,200 HP, if you delegate at ten percent, you are still at 1,080HP (1,200 minus ten percent, or 120). If you want to keep growing in your personal engagement, you want to keep growing the HP you hold. Now, nobody is going to punish you if you delegate more than ten percent ... it's just a good gauge so you keep at least 1,000 HP on hand. If you have 2,000 HP on hand, sure, you could delegate half and still be at 1,000HP, but the amount you have delegated out will be building up other accounts' voting and engagement power and not yours for the moment. Fifty percent is a lot to have delegated when you are still in early building stages.