The key here is to be flexible. Work with your printer and ask them sizes that are press efficient for them.
If you find that a size you want to use isn’t press efficient then be willing to tweak it by ¼” here and 1/8” there to match your printer’s cutoffs. that could save you a lot of money on a large print run.
It always pays to talk to your vendors about alternative size possibilities in order to achieve a better fit on press, especially in web printing. Remember, you are dealing with fixed cutoff dimensions combined with variable width dimensions. As a result, a slight tweaking one way or another can have a dramatic effect on press efficiency.
As an example, a graphic artist I once worked with designed a brochure at 16″ x 27″, but the printer recommended changing the size to 17″ x 25-7/8″. In doing so the printer was able to achieve a perfect fit on a half-web press instead of running sheet-fed, which reduced our costs by $3,500 on a quantity of 60,000 brochures.
You can save yourself a lot of time, money and headaches if you ask your printer for press efficient sizes and pass them along to your graphic designer before they start their work. If you wait until they’ve completed it before you’ve checked on press efficient sizes then you’re also putting your deadlines at risk along with the wasted time and money.