Reducing their ability to observe and interfere. The islands have always been an issue and Iran uses them as part of their control network. Denying them the smaller Islands certainly helps to keep the Straits open. Really the bigger island of Qeshm would be ideal to wrestle from their control, but I don't think the US have the troops to do that, unless the islanders raise up, as I recall there were protests there early on. The IRGC does not have limitless resources either and 80 million+ people in the country that would like to see them dead. I believe they are using up their existing resources and are going to struggle once that stockpile is gone.
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