Generally, it's very limiting that players cannot stop the Resupply operation (with partial resupplying or even without resupplying at all) - it's the most obvious operation that players should be able to stop immediately (or almost immediately) but perhaps other operations (eg. Repair) we should be able to stop as well.
BTW, I feature-requested it quite a long time ago so I hope it's just a reminder
![Smile :)](./images/smilies/icon_e_smile.gif)
Edit: I will show you an example from my pre-.77 game of how limiting it can be in case of ISRU:
I send a small fleet of Missile/PD Escorts with Advanced Pulsar and ISRU to Saturn (as to defend my colonizers and new habs they start) and in the optimal window it's less than 10-month trip while using propellant for about 36 km/s DV so my tanks are almost dry when I get there (I want to be there as fast as possible to minimize the chance of them being intercepted during travel) forcing me to immediately land and refuel by ISRU - I don't need their tanks full to make them combat capable again (I need propellant in only 1/6 to 1/3 of their tanks for combat) so waiting until ISRU makes them full again is very suboptimal and can lead to very dire consequences for the entire colonizing mission.