Future Perfect Tense

[Satyr]

1. You use the future perfect to describe an action or event that will happen in the future before another future action.
Example:
Él habrá terminado el trabajo antes de que el día termine.
=> He will have finished the work before the end of the day

2. Future perfect may also express probability in the RECENT past.
Example:
¿Lo habrán hecho? => I wonder if they did it.
Habré ganado. => I must have won

My question is how common is the second usage? And is there other ways to express the same thing?

[Rusty]

They're very common.

If you want to say I wonder, you'll use the future tense. Note these differences:
I wonder if they'll do it (soon). = ¿Lo harán?
I wonder if they did it (earlier). = ¿Lo habrán hecho?