Playing as Jill Valentine offers unique interactions and assistance from Barry Burton, a fellow S.T.A.R.S. member. His presence can significantly alter certain encounters and even provide powerful weapons.
Barry will often appear at key moments, such as your first zombie encounter, or before the Plant 42 boss fight. If you make certain choices (e.g., giving him back his gun when prompted), he will provide you with the .357 Magnum and some ammo during the Plant 42 fight, making it much easier. He also plays a crucial role in unlocking the 'Good' ending for Jill, requiring you to ensure his survival throughout the game. Pay attention to his dialogue and any prompts for interaction, as these often lead to beneficial outcomes.