You will most often encounter `罪恶` in writing or formal speeches discussing law, justice, history, and social criticism. For example, a news report might talk about a `罪恶的交易` (a criminal/evil transaction) or a documentary might explore the `战争的罪恶` (the evils of war).
The term is also used to describe a deep, personal sense of guilt over a serious transgression. The term `罪恶感 (zuì'è gǎn)` means “a sense of guilt/sinfulness” and is much stronger than feeling sorry for a small mistake. It implies a burden on one's conscience.