If we decide to create variables we should consider all of the widgets which use same variable sets on dashboard load. We can only grouping charts with rows not variables. This affects performance negatively and looks mixed because all of variables shown together in single line.
For example If we want to monitor all of layers of the system each layer needs different variables in detail with single dashboard.
First layer may be related with application side and variable selection related with it,
second layer need different db specific variables for the database layers on same dashboard. If someone opened a row then variables should load after that, if it closed it should not affect dashboard performance.