I've come to the conclusion that the discrete interface of the keyboard and keypresses meshes well with the discrete nature of text versus the analog control the mouse gives. When selecting by individual characters/lines, I'd much rather use my keyboard and know that for each keypress I'm interacting with some X amount of text than fumble with my mouse until I get exactly what I want selected. Vim keybindings specifically are nice because they provide a pretty universal interface - most applications I use implement Vim keybindings, so there's very little context switching when working with my IDE, CLI file browser, Firefox w/ Vim Vixen, etc.
Also, I find that preventing constant movement from the keyboard to my mouse and back helps mitigate wrist pain and discomfort from long sessions at my PC.
Also, I find that preventing constant movement from the keyboard to my mouse and back helps mitigate wrist pain and discomfort from long sessions at my PC.