Yeah it is useful. However the problem arises when you share a notebook with someone and they just can’t get it to work either because you forgot to reorder cells or your output depended on some state from a cell you deleted thinking nothing depends on it. You need to restart the kernel and run the notebook all the way through to be sure. Pluto’s reactivity eliminates this issue altogether. It’s a readily reproducible artifact. The functionality you mention would be the default in Pluto btw. Something that reads a sensor will read it only when you run the cell and update all depenents.