>>31639270In singles it's used to scout (Specially if your pokemon has a x4 weakness you want to avoid), gain Leftovers recovery or Leech Seed recovery, to gain safe speed boosts if you have Speed Boost or to have a safe turn for Wish to heal you. You can also delay terrain or weather turns with it.
In doubles the entire meta revolves around Protect, it prevents double targeting, allows you to use moves that hit all targets without hitting your other mons and it also lets you scout if you double protect.