Similar to how we have Line/Lines, the Bars mark uses a PatchCollection for more efficient drawing. (Unlike with Lines, we don't need to reduce the mappable properties). This can have a substantial effect:

x = np.linspace(-3, 3, 1000)
y = np.exp(-(x ** 2))

%time so.Plot(x, y, color=x).add(so.Bar()).save(io.BytesIO())
%time so.Plot(x, y, color=x).add(so.Bars()).save(io.BytesIO())

CPU times: user 2.66 s, sys: 20.3 ms, total: 2.68 s
Wall time: 1.65 s
CPU times: user 918 ms, sys: 12.3 ms, total: 930 ms
Wall time: 397 ms

The default property values for Bars are also a little different: width is set to 1, edges use the patch.linecolor rc parameter, and edge widths are automatically set using the same approach in histplot to scale down for a dense plot.

so.Plot(diamonds, "price").add(so.Bars(), so.Hist())