Awhile back at work, our team had our macbook pro optical drives removed and replaced with SSDs, with the OS transferred to the SSD. As such, the Photoshop scratch disk fills up sooner. I moved everything to my storage disk but wanted to keep the drive as clean as possible. A word of warning: the following commands permanently remove directories, so be mindful of your typing. Two simple steps, first removing my ~/downloads directory, then alias it to my local storage drive:
sudo rm -rf ~/Downloads/ln -s /Volumes/store/downloads/ ~/Downloads