Wireless networks are easy to configure on the Mac, and doing so improves connectivity. Delete the ones you don’t need, set them in the order that you want them used, and your Mac will quickly connect to the Wi-Fi networks at the top of your list.
We all have times when our Mac wants to connect to networks we don’t want it to use. At work, I would connect to a network, then months later, IT would install a newer (better) one. If I added the login credentials for the new network, my Mac would prefer to connect to the old network unless I organized the list in System Preferences.
Then, if one network that is preferred is down, your Mac will connect to one of the secondary networks. This eliminates distractions from your work and leisure, since your Mac won’t pester you each time a network is down, or it defaults to a slow connection when a faster one is available.