They remove one small source of user error.
With a tub, you need to measure the stated serving.
That isn’t difficult, but it relies on you actually using the scoop properly rather than throwing in whatever amount happens to look right.
With a sachet, the serving has already been portioned.
Open it.
Add it to your bottle.
Drink it.
That becomes particularly relevant with caffeinated products.
Caffeine has a clear dose-response relationship, but more caffeine doesn’t automatically mean more performance. Larger doses can also increase unwanted effects such as anxiety, gastrointestinal discomfort and sleep disruption.[1]
So I quite like the certainty of a pre-measured sachet in situations where I specifically want the strategy to be repeatable.
That might be a competition, a race or an important training session.
At home, accurately measuring a scoop is hardly a major challenge.
But when I’m standing beside a car at 6 am before a race, simplicity becomes more valuable.