If I want to buffer a street in ArcGIS Online, I can query it by name. So, a specific feature or segment can be buffered. If you make it its own layer. Works great just like you'd expect.
What if I want to graphically select some features? For example, with a lasso. That is often far quicker than selecting by query. I would expect to be able to select features and then run any of the geoprocessing tools on them. Then it should operate only on the selected records. This enhancement would also apply to select by filter query, so geoprocessing tools should only operate on selected records. Derek Law suggested creating a new Idea for this as an Enhancement as it is not currently a functionality and so I have created this here. I think this would be a great addition.