Flat drywall trowel vs. curved trowel. When to use one over the other?

When I say "bathroom wall," I don't simply mean the wall in and around the shower. I mean tiling every inch of every wall of the bathroom.

Here are some examples of what I'm talking about.

What are the reasons that one might tile the walls of a bathroom? I've never managed to make my bathroom walls wet in my entire life, so I see no benefit there.

Is it done purely for appearance then? If so, is there a general consensus that tiled walls are a luxury? Or, is it more of a personal preference thing? I assume that it may not inherently be considered an upgrade, as there are probably some tiled walls that look worse than regular ol' drywall.

The downside of tiled walls is the significant added price of labor and materials. Also, I feel that tiled walls age rapidly. Unless you get the most boring, square, white tile imaginable, your tiles' style/shape/size/color can make your bathroom look dated in a few years. Untextured drywall is of course ageless.

Are there other downsides or concerns to think about?

Are there instances when one really should consider tiling a particular bathroom's walls?

Redditors who've tiled your walls, what swayed you?

/r/HomeImprovement Thread