Intensive care units (ICUs) are specialized departments designed to provide comprehensive care and continuous monitoring to critically ill or injured patients. These units are equipped with high-tech medical equipment and staffed by specially trained healthcare professionals. Due to their high cost and limited capacity, ICUs often pose a bottleneck in the patient flow, making efficient use of ICU resources a critical concern for both hospitals and patients. Especially hospital departments with a high proportion of intensive care patients do sometimes express the wish to reserve ICU beds exclusively for their patients. This reservation policy can be a source of debate and controversy, as it can affect the overall performance of the ICU. To investigate the advantages and disadvantages of such a policy, this study first develops a discrete-event simulation model of the current patient flow in an ICU based on real-world data from a Bavarian maximum-care hospital. On this basis, the effects of bed reservation for certain departments will be analyzed in a scenario as well as the impact on the overall performance of the ICU to provide decision support in this regard. We show that reserving capacity for specific units results in benefits for them at the expense of performance losses for the whole system. In our sensitivity analysis, we are able to quantify these effects.