If your circ rules allow a patron to have more than one hold on a biblio, the holds interface on the intranet will provide a "Holds to place (count)" box. Koha will make as many holds as you tell it to. If AllowHoldPolicyOverride is off, the number of holds will be limited by the circulation rules. If there is not a limit set in the circulation rules or if AllowHoldPolicyOverride is enabled, there is no upper limit on how many holds Koha will endeavor to make. This presents an issue when a user inadvertently scans a cardnumber into the "Holds to place" field and sets Koha to the task of creating 21,825,001,569,628 holds. We should put some hard limit in place here. We addressed a similar issue for item creation in bug 34146.