Because Hand Traps are incredibly prevalent in the current metagame, getting info on what your opponent is holding and what cards you have to play around is devastating
Modern Masters 2017 March brought us this years Modern reprint expansion
Kraul Harpooner "The might of the undercity guides our spears!" Kraul Harpooner does a lot at just two mana
With that mode, your creatures get +1/+0 and trample, and they can attack right away, so even random dorks and tokens start to push real damage through chump blocks
Basically, it allows to change, once per turn, an Ultra Beast in the Active Position for another one in the Bench , which serves to optimize resources by not having to waste Energies in retreats and changes, and saves space in the decks by not depending on cards like X-Speed or Leaf to save retreat cost