plot() : Generic function for plotting of R objects.

plot.new() : This function causes the completion of plotting in the current plot (if there is one) and an advance to a new graphics frame. This is used in all high-level plotting functions and also useful for skipping plots when a multi-figure region is in use.

plot.design() : Plot univariate effects of one or more factors, typically for a designed experiment as analyzed by aov()

这么说吧，就像head()函数和tail()函数一样，是完全干不同事情的函数。

查看官方文档就知道啦，里面解释很详细