Ability to apply Excel-like functionality (especially the mass update, conditional color coding and real-time filtering) to any Salesforce list view or report. It makes cross-object inline editable lists possible.
We have experienced some issues with application updates being auto applied, which can cause confusion for our users when the interface changes. Minor change management issue, but better notice of updates with optionality to apply them would be a better practice.
We are using ActionGrid for more efficient lead management. The ability to create and display filtered lead lists, together with related lists in a reading pane, and then either mass update across multiple rows or open an on-the-fly defined subset of lead records, then List Browse through those records is a definite efficiency enhancer.
We also use ActionGrid for a weekly process where the Rep claims sales credit for various KPIs on their Opportunity based on submitted orders associated with those Opportunities. Another use is account and territory planning, aligning objectives with opportunities. In all cases, this allows us to combine cross-object data display with inline editing for significant efficiency improvements.