Should the Play Store be hidden or shown on managed devices?
It is a policy choice. You can hide the Play Store so users only get apps you place on their list, or show it where people need to browse. Hiding is the usual choice for younger students and shared tablets. Showing it does not widen the app list, which still decides what stays on the device.
The Play Store is shown or hidden by policy only. With it hidden, a student has no way to browse for new apps, and no way to spend money inside the store. With it shown, they can look at listings and try to install, but the app list and install guard still apply.
That last point matters. If the Play Store is visible and a student installs an app that is not on the list, the install guard removes it silently. Unknown sources stay blocked, and alternative browsers, VPN apps and proxy apps remain blocked whatever is shown. So showing the store is less risky than it sounds, though it can still cause noise and confusion.
Most schools hide it for junior and middle classes, and for exam and demo tablets. Some show it for staff devices or for senior groups, where a teacher wants people to find an app and ask for it. In a company, hiding it on field phones keeps staff to the approved set.
To add an app for someone who needs it, use the app list and the organisation app store, not the Play Store on the device. A practical tip: set the Play Store choice in the organisation defaults, hide it by default, and show it only for groups that have a reason. Use the effective policy view to confirm the final state on a sample device.