Large objects, why not use the filesystem?

Greetings,

I always see posts of people trying to get their large binary and text
objects into and out of the database somehow.  I was wondering if there is
some reason why just storing a filename in the table would be a bad thing?
This way you can let the file system worry about storing the data (since
that is what the file system is good at.)  I understand that you probably
could not access the data via ODBC, but if you are writing your frontend in
C or Perl, etc. then you would simply use the filename stored in the table
to access the data.

Comments?

Also, could someone explain varchar?  I have never found a *really* clear
explanation and I'm not sure I fully understand its potential, use, and/or
shortcomings.

Thank you,
Matthew Hagerty