Q:

prevent custom text to increase plot size

I am writing some text on my plot, which works perfectly fine.  Now I realized that if I put the text further down the y-axis, the plot space somehow becomes larger.  This is not what I want.  The following 2 plots illustrate the issue.  The first one puts the text at y = 0, whereas the second one puts it at y = the min-0.25, so roughly where the plot space begins vertically.  Is it possible to keep the plot space as in the first plot, but still to write at the bottom?  If there is no intended way to adjust that, I would also be happy with a workaround.  
set.seed(12)
test <- data.table(x = rnorm(29*2),var=c(rep("x1",29),rep("x2",29)),
                   time=rep(seq(as. Date("1983/12/31"),as. Date("2011/12/31"), "year"),2))
library(ggplot2);library(scales)
ggplot(data=test,aes(x=time, y=x, colour=var)) +
  geom_line() + scale_x_date(date_labels="%Y",date_breaks = "3 years") +
  geom_text(aes(x=as. Date("1988-04-30"), label="Text which does not increases space", y=0,
                fontface="plain"), angle=60, colour="black",vjust=0,hjust=0,size = 4)

ggplot(data=test,aes(x=time, y=x, colour=var)) +
  geom_line() + scale_x_date(date_labels="%Y",date_breaks = "3 years") +
  geom_text(aes(x=as. Date("1988-04-30"), label="Text which increases space", y=min(test[,x])-0.25,
                fontface="plain"), angle=60, colour="black",vjust=0,hjust=0,size = 4)

A:

As any other geom, geom_text expands the plotting area in cases like this.  Then it's necessary to manually restrict the y axis with ylim(range(test$x)).  However, that's not enough, as then the text wouldn't be fully visible and, as a result, ggplot completely drops it.  To fix this, we need clip = "off".  Thus, adding
coord_cartesian(clip = "off", ylim = range(test$x))

gives

where now axes are unchanged.