There might be very rare cases where hitting yourself would have a clear tactical benefit, depending on how your DM rules
There is one scenario I can think of where you might want to hit yourself with an attack roll, and that would be to get the effects of the Absorb Elements spell -- which you can cast only as a reaction to taking elemental damage.
Why would you want to make this happen? Suppose you want to enter a room and make someone think your sword has the power to create a burst of damaging fire when you strike, and by the way you have the fire bolt cantrip. (You don't want to look like a wizard; you want to fool them into thinking you have a magical sword.) You might decide it is worth it to inflict a little bit of damage on yourself from your own fire bolt to have the occasion to use Absorb Elements: the result is that your next strike with your weapon adds fire damage.
So you want to fire bolt yourself. This might seem silly, but the point is, you have some motive for charging your weapon with Absorb Elements, where there's no ready way to do so but to hit yourself in this way.
Now your DM might say you can auto-hit yourself, but I don't think self-hitting is covered in RAW, so a DM could rule otherwise. Inanimate objects even have an AC that must be overcome to damage them ("hit" really means hitting something good enough to do it damage) -- so it is conceivable that the DM might say you have to beat your own AC (or at least, your armor's base AC without any Dex bonus) owing to the fact that your armor still protects you somewhat from striking yourself.
So if your DM rules that way, trying to use fire bolt on yourself might not work if you have to roll a 16 against your own chain mail. But if something else gave you advantage on hitting yourself, it would help. So there's the usefulness, finally, for saying you have advantage on hitting yourself.
Very much an edge case, but not impossible.