What does the information ratio on its own tell you? Is it supposed to be in relation to something usually?
In the simplest sense, how much risk a manager needed to take to generate an active return. They are typically used to compare portfolio/fund managers, say if considering them for inclusion in a particular portfolio asset class - generally speaking you will aim to compare managers with reasonably similar styles and investment universes though this is not a hard and fast rule. Alternatively, for an individual manager it can be useful to monitor the information ratio over time to help assess how their portfolio construction/bets are evolving.
Source: used to work in asset consulting. In reality not a huge deal of emphasis was placed on IR in the manager selection process, small component of a much larger research piece.