Space Bar gives you a lot more insight into the space of your fonts, specially when you are working on a font with multiple masters. It shows you the defined instances of your font and they are represented by curves. So you can work on one master but controlling somehow the other master values and the general project.Space Bar makes information visible, is a visualization tool.
This plugin compared anchors used in two different fonts. Shows in light orange the anchors used in the glyph of the next font and in gray the current font anchors. If names and quantity matches it will show a “Ok” message in green.