It doesn't matter for coding or functionality, but it is nice when you're manually eyeballing the results of 'SELECT * ...' statements or browsing tables with something like Navicat, or looking at schema dumps - to have your fields ordered in some way that makes sense to you, rather than strictly in the order they were created.

Sure, you can list the fields in the order you want in a SELECT statement, but that's tedious - it's handy to have something reasonable in the table definition.

There's a wiki page on the Postgres site:

https://wiki.postgresql.org/wiki/Alter_column_position

talking about workarounds and a plan from 2006 on how they might implement that feature.