The Legend of Korra

On he metalbending thing:

I think Lin had to ground pound because she isn't nearly as sensitive as Toph was. Toph pretty much used seismic sense her entire life to "see", which is likely how she can detect so easily (even without a ground pound). It's so ingrained in her way of life that it's practically second nature for her to continuously use it. However, people like Lin, while they know about it, aren't exactly using it 24/7; like everything else, the technique has retained it's high master level, unlike lightning bending. They probably use the ground pound to create a larger seismic wave to make it more pronounce to them. Toph could easily have done the same thing, but she's more likely to be extremely sensitive to every single small movement that causes a vibration and wouldn't need a big huge seismic wave to sense things.

Also they probably wear shoes cause they're like humans in real life. People don't go walking barefoot on sidewalks. I'm sure they could use seismic sensing with shoes on, but it's probably easier to sense without shoes. Hence why toph is barefoot all the time.