I participated in rituals that people referred to as casting spells. Did I ever think I had personal supernatural powers? No. Even while fully in I thought of it as focusing my intent and visualizing the results I wanted, with the idea that if my goal was in harmony with the Goddess (or God, or any of multiple aspects considered of a general Gaian divinity), that it would be more likely to manifest, although probably in ways that did not appear supernatural.
We were taught to visualize not a specific effect, but the outcome we wanted-- whatever specific healing, justice, wisdom, protection, courage, that sort of thing.
The most useful part of the exercise, I think, was having to decide what you actually wanted and being receptive to it should you find it available. A lot of people don't accept what they want even when it's staring them in the face, like the old joke with the overboard priest that spurned a ship and a helicopter. Maybe also a little extra confidence to actually move towards making things happen that you want, in completely non-magical ways.
Ultimately, along with starting to read more about skepticism, I realized I didn't really believe in a pantheistic or nature divinity any more than the Christian God, and that I could keep the friends, the ethics, and the useful portions of "spellcasting" as I described above, without playing along with any supernatural ideas. So I went back to atheist.
"If fighting is sure to result in victory, then you must fight! Sun Tzu said that, and I'd say he knows a little bit more about fighting than you do, pal, because he invented it, and then he perfected it so that no living man could best him in the ring of honor. Then, he used his fight money to buy two of every animal on earth, and then he herded them onto a boat, and then he beat the crap out of every single one. And from that day forward any time a bunch of animals are together in one place it's called a zoo! (Beat) Unless it's a farm!"