RIGHT NOW there is no problem. However, as more and more data is built and more and more dimensionally-tracked data is needed, Epicor MAY at some unknown point in the future decide to use this field for an actual “thickness” dimension calculation. If it ever does so, you’re screwed. What is he likelihood? In this case, probably pretty small… but since UD fields are so easy to create (yeah, even in the cloud it’s not that much of a hassle), why take the risk?
That is the Best Practice argument.