I know this is not a racing thread - but it applies.
We now just use water, then packet GU/food for electrolyte.

On a hot day the option to squirt water on head/back is nice. We remember the chocolate milk mistake.

The ideal concentration of a mix/water varies with temperature. Having a pack and washing it down lets the ratio be controlled on the bike.

You can share in picking up bottles for others. If they are all water, anyone can take any and use their sauce and wash it down.