Preflight is very important. I really never knew much about it before I started working my first job as an Art Director. In this position I had to flightcheck all projects before we would send them to the printer. Basically, if there were any issues it would come back to me as I was the one that did the final checks.
In the beginning I was very confused by the process as I found so many issues alerted I, that I was told just to ignore. With more experience I learned what issues would cause problems and which ones would not.
One key thing to keep in mind of why flightcheck is important is it will make you aware of issues that you may not have even considered. One time I was running fight check on a project to send out to a specific printer. This printer had sent me their personal settings for the flight check software, and would make sure everything was setup to their specs.
When running this project through I found that many of the gradients in the design did not meet the standards for the printer. In this case the printer wanted no color less than 10% or it would not show up. The gradients were created with 10% color, and would not show up at all.
While I was not the one that created the gradients, I would have been the one that got nailed with missing this detail when the project didn’t print correctly. I was able to flag this issue and got the company that created the gradients in some hot water.
Fight check is a great last step to ensure you will have the print you are looking for. If you don’t flight check you will probably end up making multiple trips to the printer as little details easily slip by, and affect the print. I have found something as silly as not having embedded images and not including them with my print package has wasted my time as well as the printers.
As far as checking it yourself, without software assistance, I don’t suggest it. The software is there, USE IT! There may be a small issue that you are not even aware of.