Opportunistic feeders, their diet varies from one region to another. In the Antarctic, killer whales eat about 67% fishes, 27% marine mammals, and 6% squids. Killer whales in the Bering Sea (near Alaska) eat about 65% fishes, 20% squids, and 15% marine mammals.
Even though your shower grout looks dry, using it too early or sealing it before it's ready may damage it, leading to premature failure. Most cement-based grouts require a cure time of 48 to 72 hours before applying a penetrating sealer.
Short answer is no, you don't NEED to seal the grout. Grout sealer is one of those products that manufacturers try to sell people that really aren't the best idea in the world. The pitch is that it will prevent mold forming. Well, that is only true in the very short term.