It does rely on input from users for things such as stranded cars, police cars, etc, but it is still a good navigation tool without the direct input as it uses the speed data from users to identify slowdowns without the users inputting data directly. You may see a slowdown indicated, but not know why it is occurring until a user indicates a crash or something else causing it.
The only time I have actually entered data while using Waze was having my passenger enter the data. I'm sure not everyone does it this way, but I prefer to be as safe as possible while driving so I don't text, read a book, etc while driving.