At a conference, should I visit other people's posters during my poster session?
It depends on the venue. In a small room, you can easily wander around and get back to your poster quickly if you spot someone interested. In a huge conference hall, if you abandon your poster you may never know who visited it and when.

So, if you have a large venue, ask yourself, what is your priority: to get your work out and have a chance of presenting yourself, or to check out what others are doing. Both are valid options, and both are important. It's your call how to balance them.