It really depends on what language you’re using, but in C# and Java I find IDEs beneficial for:
- Quickly navigating to a type without needing to worry about namespace, project etc
- Navigating to members by treating them as hyperlinks
- Autocompletion when you can’t remember the names of all members by heart
- Automatic code generation
- Refactoring (massive one)
- Organise imports (automatically adding appropriate imports in Java, using directives in C#)
- Warning-as-you-type (i.e. some errors don’t even require a compile cycle)
- Hovering over something to see the docs
- Keeping a view of files, errors/warnings/console/unit tests etc and source code all on the screen at the same time in a useful way
- Ease of running unit tests from the same window
- Integrated debugging
- Integrated source control
- Navigating to where a compile-time error or run-time exception occurred directly from the error details.
- Etc!
All of these save time. They’re things I could do manually, but with more pain: I’d rather be coding.