Potions are not just magic beverages -- the exact same rules apply to magical oils, a seldom-used but equivalent option. You can smear an oil on just as easily as you can drink a potion. The only difference is that when you drink a potion, you are the caster and the target of the spell ... but when you apply an oil, you are the caster and the thing you smear is the target.
That offers three options for oils:
- Smear on self: this is exactly the same as drinking a potion.
- Smear on another creature: this is like casting the spell on the creature.
- Smear on an object: this is for spells that cannot be cast on creature but can be cast on an object.
Note that oils offer two different functions that potions do not. You can smear an oil on a thing, such as applying an oil of Purify Food and Drink on a rotten roast. You can smear an oil on a friend, such as dousing a pal with an oil of Barkskin.
Honestly, since it costs the same, no one should buy or make potions of Cure Light Wounds ever. You should only make oils of Cure Light Wounds. Those can be applied to yourself or to others as a standard action. If you want a friend to use a potion, the only option in the rules is dribbling it into an unconscious person's mouth as a full-round action. Better to just smear the fallen friend with an oil (also a full-round action), or rub the friend before they fall while he fights the dragon, so that she does not go unconscious.
Note that the rules are very lenient in who can use a potion or oil: "Drinking a potion or applying an oil requires no special skill. The user merely removes the stopper and swallows the potion or smears on the oil. ... A creature must be able to swallow a potion or smear on an oil. Because of this, incorporeal creatures cannot use potions or oils. Any corporeal creature can imbibe a potion or use an oil."
And of course, you can yourself apply oils to familiars, animal companions, and mounts, who would themselves have trouble uncorking a potion or drinking out of a bottle.
So to use a potion you need to be able to remove the stopper. That requires a certain degree of manipulation. Can your cat familiar uncork an oil and smear it on you? No. Can your monkey familiar? Surely yes.
Familiars are relatively useless in general. Too poor in combat to be viable warriors. Cannot speak, so cannot use any command word items or scrolls. Well, the raven can speak, but lack of hands is a problem there. But this! Opening an oil and smearing it, seems well in the range of a familiar monkey, say. Now the familiar becomes quite useful, applying oils to its master and even to allies. And since you do not have to take actions, except maybe the free action of giving your familiar commands, you are still free to engage your full range of movement, casting, and so on.
I'm thinking I need to make a mage character with a monkey familiar who smears oils on allies. Maybe the monkey can have a tiny haversack full of oils. At 5th level, a wizard can talk with his familiar, so giving orders is no problem. What the heck, make him a druid/wizard with a baboon or ape companion. Put a couple points into its Int, maybe top it off with a Headband of Vast Intelligence, and go nuts delivering oils!
One naturally may wonder, can you smear an oil on an unwilling creature? Say an oil of Bestow Curse, for example? Of Slow? Of Silence? Can you stand next to someone and splash the oil onto an adjacent target? Can you toss it as a thrown weapon? Smear it on a grappled or pinned foe? The jury is still out on that one, so expect table variation depending on how nice your game master may be. Bottom line: The rules are silent on this, so if you want to do it, you and your game master will have to come up with rules for range, attacks of opportunity, and so on, if it is even allowed at all. Arguably, standing next to a person and trying to smear them with an oil would provoke three AoOs: One to fish it out of your pack or pocket; a second to uncork and use the oil, and a third to smear the oil on the target, as a ranged touch attack with a range equal to your unarmed reach (usually 5 ft). Better hope your enemy does not have the Combat Reflexes feat!
Now, if oils are all that, why even make potions? A mean DM could rule that drinking a potion requires one hand but applying an oil requires two ...
Art credit, with thanks: https://magicgummies.com/magical-cooking-oil/