A player can choose to draw 1 card at a time for 150 gems, or to draw 5 cards at a time for 675 gems.
It is also worth to note that some card can only be obtained through the gem bag or limited gem bag events.
Some people claim they have better luck when drawing one card at a time, while other players claim they get better rewards from drawing five cards at a time. Any hard fact to prove either or would be useful.
A 5 card draw often means that you are entitled to bonuses, such as in the event of "You Draw, we Reward!" or "Premium Altar". It can also guarantee you a 4-5 star card after certain amounts of 5x draws.