libtool upgrade question (UPDATING/20060223)

[Hans Lambermont]

Hi,

I have a question about a ports upgrade method as mentioned in the
20060223 libtool entry in UPDATING.

The entry mentions :
...
  Unfortunately, there is no simple upgrade path.  Short of removing
  all packages and reinstalling from scratch, the only other viable
  alternative would be careful use of portupgrade.  Given the large
  number of different ways in which libtool is used by other ports
  in the tree, this is a process that is likely to vary considerably
  from system to system, and as such, folks should be very mindful
  of running automatic updating software, such as portupgrade, making
  extensive use of the -n flag (and equivalents for other updaters)
  to see what will actually be rebuilt, before actually performing
  the upgrade.

I'm wondering what the 'careful use of' really means, more specifically
what should one look out for when using the mentioned '-n' ?

regards,
   Hans Lambermont