The higher your tier, the more @qurator will increase its voting strength. Delegating SP to @qurator makes its votes worth more money. So when @qurator votes for your post, you get more money. Delegating means your own votes will be worth less money, but you still own that Steem and can remove the delegation in the future.

The tiers get votes with the following strengths, from tier 0 to 5.
0.5% - 1.6% - 2.6% - 4.5% - 5.5% - 6.5%

In the article, he shows what those percentages mean in dollars.