In the quest for new energy sources, the research on controlled thermonuclear fusion explores the magnetic confinement of hot plasmas. Various spatial configurations of the magnetic field have been explored. The tokamak is the one which, up till now, has achieved the best performance and where most of resources are concentrated. Alternative concepts are however actively researched. Among these is the reversed-field pinch, where a spontaneous transition to a helical equilibrium occurs, with a change of magnetic topology resulting in improved confinement (Lorenzini et al., Nature Physics 5, 2009). This transition is an elegant example of plasma self-organization towards a 3-dimensional helical state. Starting from this result the talk will highlight how 3D helical structures, which were in the past often considered the result of instabilities and therefore to be avoided, might be an important and useful feature of magnetically confined fusion plasmas.