What is a PH streak good for?

It serves as a sign to other Product Hunt users, indicating your activity and involvement within the community. Additionally, it can serve as a personal motivator.

In order to get into the top 1 in terms of activity, but this can also act as motivation.

I think that it shows other hunters that the person is active, therefore they are more likely to connect with you especially founders who are launching soon. also it keeps the pressure to be active by giving you little rewards like badges. I don't think It's necessary but I guess these are the use cases.

Besides ranking, it is also good for self discipline. Keeping your streak is definitely a commitment.