Do I need to get Botox regularly to maintain the effects?

I am looking into Botox for wrinkle or facial contour management, and I am wondering if it is a one-time treatment.
It seems like you can start without any pressure at first, but if you have to keep it going, I realized you also need to consider the cost and time involved.

For those of you who have received it personally, how often do you usually get it done?
I am also curious if the actual management period was similar to what was initially expected.