This is for projects that need critical path functionality / GANTT charting (i.e. if one task slips, it pushes back the dates of all subsequent tasks). We tried Asana, Basecamp and Trello, but none of those allows you to define the duration of a task, or separately input start and end dates, and create dependencies.
We are a hardware startup, so we need critical path functionality to determine manufacturing timelines.
The spreadsheet-like UI is very easy to use. However, the disadvantage of the UI is the spreadsheet cells aren't enough for discussion or comments. You can add comments to each row, but it doesn't have the great discussion features that Asana has.