I have used it to park in tight spots. One example is two cars parked such that my car blocks only their passengers' sides, but they leave not enough space for me to open my door. Then I back into the free space half way, exit from the car and remote-control the remaining half car-length.
The other, similar situation is that I park somewhere and other cars later park very close, such that it is difficult or even impossible to open my door wide enough to enter.
In one case an elderly woman squeezed her car into a narrow parking space next to my car and then found it rather difficult to open her door wide enough to exit conveniently. I could quickly and remotely pull my car out, so she could get out more easily, then I remotely parked my car into the same spot again. We went into the same shop, such that I could have repeated the operation, had she left the shop before me, but in that case I was out first. I guess after that the lady had a story to tell, which is good for Tesla.
Yet another situation is a tight parking space and a passenger. I could quickly pull the car half-way out of the parking spot to let both me and my passenger enter the car. (I customarily park backwards.) Actually in any tight parking spot it is easier to open the doors widely while the car is not fully parked.
When exiting a parking spot, it can be even more convenient to call the car out into a place where there is room all around.
I admit that these cases for Summon are infrequent, but I still miss the capability. I swapped my Model 3 for a new one and found that in a used Tesla FSD is not fairly priced in. So I cannot buy FSD again and again when I swap cars. There are other capabilities in FSD that I also miss, among them automated lane changes, NoA, and auto-park. As soon as Tesla keeps FSD with my account, rather than with the car, I will immediately buy it again. That could be a quite effective way for Tesla to keep customers in the brand.