Svn:externals with -r or without?

Rails
1

I have finally moved to svn for managing my rails applications.

After running the svn:externals propset for edge rails i realised that
this will be updated every time i run update.

What is common practice for this, does one add the -r to specify a
version, thus ensuring that an udpate wont download a edge revision that
will break your project.

or

Is it more common to leave it to auto update then roll back a revision
of edge if you have problems ?

2

Also, for installing plugins in your working copy is it better to just
run plugin install then svn add.

or

add the svn:external prop to add the repository ?