I write them on and off, mostly whenever I feel like it. Without outing my pseud, I love to put my emotions into characters I love and putting their perspectives in situations I feel like I need another perspective on, especially mental health, suicide, and sexuality. Once in a while I write crack.
It sucks hitting a writers block and feeling unable to write, but also that writing fanfiction is mostly for myself and nobody else. Easier said then done of course, but I use it mostly as a form of self care.