For example, playing this white human cleric into the next card means you can cast a 3-drop and then still end the turn with 1 energy
Others can join in the Round to increase the power of the attack
Some of my favorite effects to double up on are Fervent Charge, Mardu Ascendancy, and Brutal Hordechief, and those are just the Mardu-aligned ones
Additionally, Lighting, Army of One has Lifelink, Trample, First Strike, and Staggering, which cause other damaging effects to double against an opponent or their permanents for one turn after she attacks
Suddenly your 4/4 is a 6/6 that gives all of your permanents hexproof - which is absurd on its own - and then also puts two +1/+1 counters on each of your creatures at the beginning of combat on your turn
Limited players are stuck with Draft boosters, now replaced by Play boosters but that isnt necessarily a bad thing