MTB: choosing trajectory (line) through a turn
Cornering is an essential mountain biking technique, regardless of the type of turn you're going into.

Scenario 1: Turn to obstacle
With clear visibility you should make the turn so the exit lines you up for how you plan to ride the upcoming obstacle. Usually this means taking the turn wide (high) so you can pull the bike back into line easier.

Scenario 2: Single turn
A single turn leaves you with only one decision: fast or slow? The lower you go through the turn, the tighter the radius and the more speed you will carry (conservation of momentum). But like any type of riding, maintaining control at speed can be difficult, which may cause you to take a wider line.

Scenario 3: Turn to turn
Consider an S-curve. You'll want to kind of approach it with the idea of slaloming through the turns. This means picking whichever line will bring you into the entrance line of the next turn. Again, this usually means riding further out, then coming back in to the entrance of the next turn.

Lastly, as you mentioned in example 1, there are times when the other side of the berm isn't so pleasant if you happen to overshoot. Here it's about how much courage you have! If you have the skills and want to ride high then go for it, otherwise scrub a little speed and take the tighter line. And really, there's always the ideal situation, then there's what happens on the trail, which is often very different from how the ideal works.