Most PDF files are not created equal however. There are many different variables involved that have a negative effect on printing. Some of these include missing fonts, missing images, and color space issues.
Checking files is essentially used to avoid problems in processing or printing content. This can be done through preflighting your files. The earlier in a process that issues are detected, the easier it is to fix them. This implies that designers should preflight their designs before sending them to their agency or printer.