I won't use salt at all, because I have planted tanks and worry about build-up as I don't completely change the water, ever.
I think the main concerns with using salt are long-term damage to fish organs, as well as saline buildup if the water isn't changed completely every time. Personally, I don't think it's necessary, especially if your water's kept nice and clean and you have lots of plants and a good bio filter to help the water quality along.
That said, lots of folks swear by tiny amounts of salt in ratio to water volume and have healthy fish. I wouldn't do it, but if your fish lives a long and healthy life and it's working for you, then there's no problem, I guess.
eta: sorry, just noticed that you've got a really small tank there, it's such a tiny amount of water that 1/4 tsp of salt would be a lot.. I'd actually be worried about using that much salt..