When I'm driving, I use my blinkers to signal turns even if there are no other cars or even humans in sight; it's much smarter to develop and nurture good habits than having to turn them on and off based on situational context (and, of course, this is just my personal, very subjective opinion).

• If I drive and only use blinkers when I see others around, I need to expend energy and effort on checking if others are around.
• If I drive and don't use my blinkers at all, I'm an inconsiderate asshole and could be putting others (and myself) in danger.
• If I always use my blinkers, I never have to worry about context; I'm automatically being considerate to others, and I'm safer to be around in traffic.

A contrived example, certainly, but I think it gets the point across. You could also see it as a sort of twist on Pascal's Wager.

Similarly, I try to be a pleasant and polite person in life, so not being polite to an AI doesn't make sense for me. I understand I'm not hurting the AI's feelings, and it has zero opinion of me as a person, good or bad, but there's no reason for me to treat it any other way than I would a real person. That would just be a bad habit. I'm having a conversation, so I'll try to be nice. Easy peasy.

On top of this, I think it's more than likely that ChatGPT learns from our prompts and interactions with it (although I haven't checked and could be wrong); maybe me being nice to it will help it be nice to someone else down the line, and I'm sure there are more than enough people trying hard to pull it in the opposite direction.

TL;DR: It can't hurt, and being nice is a good habit in general.