When you will select several hosts and then close browser, your selection will remain in cookie/session. If you will several hours later open foreman using bookmark like https://foreman.koudis.cz/hosts?utf8=%E2%9C%93&search=+owner_id+%3D+17 you will see some hosts and it's possible that you will not see that some hosts are selected already, because they're not part of current filter. If you will want to delete one host, you will select it (add it to group of already selected hosts) and if you will not catch this in confirmation box, you can delete more hosts than you expect. I think that it's better to delete this cookie when you close page with foreman.