The iPad has an excellent touch sensitive screen and has never failed to respond to my touch except when I’m wearing gloves but I now have gloves with conductive material in the finger tips so even that’s no longer an issue. So you might be asking why I bought an iPad Stylus if my finger(s) work perfectly well? I bought the stylus to assist with sketching and note taking on the iPad.
I’ve never found it very natural to write or draw with my finger on any touch screen device, throughout my entire life I’ve always used something in my hand to draw/write be it a pen, pencil, paintbrush, etc. Using a stylus to draw or scribble notes on the iPad is much more comfortable than using your finger and I find it gives me greater control and accuracy over what I’m drawing.