Many experienced photographers prefer to use the DSLR viewfinder to frame photos. For example, using the viewfinder allows you to hold the camera steady against your face, which makes it easier to avoid camera shake.
With the viewfinders on older DSLR cameras, you didn't have the option of displaying some of the camera's settings through the viewfinder. Now, however, DSLRs can display almost anything about the camera's settings in the viewfinder, similar to the way data is displayed on the LCD.
The way the data and settings are displayed in the viewfinder may differ a bit from what you see on the LCD, though. Click the link to read my latest article that can help you decipher the data you're seeing in your DSLR's viewfinder.