Oh absolutely. It's like that old chestnut about plans being useless but planning being essential. And one can even find productive use for an aggregate SWAG-

Oh absolutely. It's like that old chestnut about plans being useless but planning being essential. And one can even find productive use for an aggregate SWAG-to-reality ratio, tracked over time. Individually, that ratio won't give you any better an indication on where a given SWAG is likely to land, but in the aggregate you can use the ratio to put something like error-bars on the project as a whole.