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When you power up hive, it helps grow your hive stakes, and you earn with it whenever you support others by voting for them.

It is beneficial on multiple levels.

With higher amount of Hive Power, the value of your upvotes are also higher, your curation rewards are also higher, and you can build additional passive income (or simply help other Hive users) by delegating Hive Power to them.

Okay is it done only one the first of every month or it can be done every other day

You can do a power up whenever you want, but the 1st day of every month is known as Power Up Day as a reminder that you should do a power up. HiveBuzz also gives you a badge when you do a Power Up on PUD.

Ohhh
I see, thank you

You're welcome 😊