With most powders in .25 Auto or .32 Auto, 0.1 grains can be the difference between a safe load, and a blown primer. An extra 0.3 grains can result in a ruptured case. With some powders in .380 Auto, 0.1-0.2 gr can be the difference between a safe load, and a blown primer. An extra 0.3-0.5 grains can make for a very bad day.
In most other cases... It's just a matter of accuracy.
"Such is the strange way that man works -- first he virtually destroys a species and then does everything in his power to restore it."