Cuándo usar un Grouped Bar Chart
You have two to four series to compare
Two is ideal, four is the practical ceiling. Past that the groups blur together and the eye stops being able to track a colour across the chart.
Comparing series within a category is the point
Which product wins in each region, whether this year beat last year in every month. Adjacent bars make that comparison as easy as it can be.
The totals do not matter
If nobody will ask what the category adds up to, there is no reason to stack. Grouping keeps every value on a shared baseline where it can be read accurately.
Values are similar in size
Small differences survive a grouped bar chart because every bar is measured from zero. Stacking would bury them in the middle of a segment.