poop,
It's not about trying to make boots lighter. The reason for the above is invasives. Wear boots in one stream, don't let em dry, then wear em in another. That's how didymo, mud snails, and other invasives spread.
You have several options. Treat them as PennKev suggested. Or let them dry, completely, if you fish enough perhaps have multiple pairs to rotate so that there's time for this to happen.
It's not an either/or situation, and I see this as a decent trick that doesn't take much effort. If you go a week or so between outings, and the boots appear dry, measure em. If they're still a bit heavy, then you gotta go with a another pair or treat em.