It should be a given. Period.
When a person takes the responsibility of being a Top to a play partner aftercare should be discussed as much as a scene or safety or limits. It doesn’t matter if you play with this person once or have an ongoing D/s relationship with them. It is a privilege bestowed upon you when someone agrees to allow you to top them.
If you feel uncomfortable giving aftercare then the discussion of other options should happen. Don’t come up with excuses or say, “I’m not good at it.” That’s a fucking cop out. If you play you can either learn to give aftercare or make sure your partner has someone on standby to give it.
A bottom should never walk away from a scene/play session without knowing they will be taken care of when they start to drop or bottom out. It’s a horrible place to be and it can make people decide not to play again. Sometimes it only takes one bad experience to keep a person from trying again.
Remember the person that trusts you during play is not a prop but a human being. Treat them with care. Trust is a massive thing to earn and to throw it away because of carelessness is not only callous but selfish. But, this is just my opinion.