Take this as the opinion of someone who did a bunch of reading, but never did any real experiments...
Overpitching is a thing that can happen, but as homebrewers, we shouldn't worry about it anywhere near as much as underpitching.
First off, if you look at what commercial breweries do, they pitch at much higher rates than typical homebrewers do. So the amount we would need to pitch to exceed the typical range of pitching rates would be silly large.
Second, the results of overpitching are generally pretty mild. You might get a cleaner fermentation, as there's less of a growth phase (that's where a lot of esters and other yeast derived flavors come from). If you harvest from the yeast cake of an overpitched batch, you might not have the healthiest yeast for the next batch. Now if you're going for a stressed yeast flavor, like a funky Belgian or something, you might be more worried about this.
TL;DR, half a packet is common practice, and nothing I personally would worry about.