createdb -D and absolute paths

[If this gets posted twice, it's because the original seemed to get
stuck in the mod queue when I wasn't subscribed.]

I read the following about allowing absolute paths in createdb:

Note: If PostgreSQL has been compiled with ALLOW_ABSOLUTE_DBPATHS
(by passing CPPFLAGS=-DALLOW_ABSOLUTE_DBPATHS to gmake after
configuration), absolute pathnames are allowed. This is not allowed
by default, due to security and data integrity issues that can arise
from using database locations specified as absolute paths.

What are the security and integrity issues?

m.