Conditions are used when button stacking or specifying what size range should be used for a certain item.

For example, one may have a button for all Shut-off Valves.  One could have a button code of SOV, and have ball valves with a condition of 0-2 & Butter-fly - Lever operated with a condition of 2.5 - 6, and Butter-fly - Gear Operated with a condition of 8+

It also specifies what hanger specification will be used for that size range.