I often find myself wanting to know the internal volume of a tank, vessel, or assembly. There are ways to do this, but it would be great if it was an additional tool built into Inventor. I envision it working like this:
1) Open the part or assembly in question.
2) Start Measurement tool (or perhaps a new tool).
3) Select faces/planes to "close". These would be things such as the maximum liquid level and ports.
4) Inventor reports the internal volume of the vessel/tank.
This is similar to an archived idea posted by @Anonymous.