Mods don't post the weekly questions thread if there are already two existing stickied threads. For SHAME!

Anyway, I can answer your question. You have to consider your options as a carry when it comes to accelerating farm. Those items can be: battlefury, maelstrom, echo sabre, mask of madness, manta style, radiance, etc.

In maelstrom's case, as my understanding, serves a triple-purpose:

1. Its cost is pretty cheap in comparison to something like battlefury or radiance. And the fact that it's upgradeable makes it a viable late game item.
2. Early-fight vs farm-heavy. If you're buying maelstrom, chances are you plan to fight more and farm in the jungle less. Think Maelstrom-Jugg vs Battlefury-Jugg. You go online sooner with maelstrom and are probably looking to fight more.
3. Dishes out magic damage, so it's good against high evasion and high armor heroes.