Unit # vs. Legal Unit

Unit # vs Legal Unit. What's the difference? When adding a new listing you are faced with two areas asking for "Unit".
Unit # under the Address tab
Legal Unit under the Main Fields tab
Unit # would only be used if the property has a number associated with the address. For example: condo or townhome unit. Legal Unit would be in the case of the legal description referencing a unit. For example: Lot 19, Block 19, Unit 4, White Mountain Meadows Sd.