When a company files as an LLC on a W9 form what would be the appropriate circumstance in which a disregarded entity would be chosen as the tax classification?

A disregarded LLC is one that is a single member LLC or Foreign LLC with a domestic owner that qualifies under Statute 30.7701-3

For an LLC that is disregarded as an entity separate from its owner, you must show the owner's name on the first name line. On the second name line, you may enter the LLC's name. Use the owner's TIN. Do not enter the disregarded entity's EIN.