[Quick-Play Spell Card]
During the End Phase of the turn this card is activated, draw 1 card from your Deck for each Dragon-Type monster discarded from your hand and/or Tributed during this turn.
Why is it the main draw engine for Hieroglyphs?
Because most of the Hieroglyph cards tribute to Special Summon themselves to the field along with a Dragon-Type Normal monster, which then can be tributed for the Hieroglyph effect. Which means, you'll get to draw 2 cards every time you Special Summon the Hieroglyph monster (by tributing a Hieroglyph monster) and every time you activate a Hieroglyph effect (by tributing a Hieroglyph monster)
What I thought was interesting was this: (Please note that I could be wrong on this)
TCG: In the TCG, the hand size limit is the absolute last thing to occur, which means, you draw for Super Rejuvenation, and after you draw for Super Rejuvenation, if you have more than 6 cards, you discard until you have 6 cards.
OCG: You can choose when you can apply the hand size limit. For example, you can apply the hand size limit at the End Phase, before you draw for Super Rejuvenation. So, you discard 2 Dragon-type monsters from the hand size limit, then draw 2 more cards from Super Rejuvenation in addition to whatever you tributed for the turn. You do not apply the hand size limit twice per End Phase.