Cleaning Ports and Apache 2.2.8 installation

[Thomas Hagedorn]

I'm on a MacBookPro,  Intel 64-bit, with OS 10.5.2.   I had MacPorts 
installed but then I wanted to test a script to do an automatic 
installation.   To do that, I ran

sudo rm -r /opt/local

and then ran the script to install MacPorts (via binary package) and 
then other ports.    I ran into an error with the command

sudo port install apache2 +preforkmpm

as  when MacPorts tried to install the dependency sqlite3 it produced a 
fatal error about a file not being accessible.  

Running the command

sudo port clean sqlite3 

helped, as well as breaking up the script into the parts

sudo port install apr
sudo port install db44
sudo port install gmake
sudo port install readline
sudo port clean sqlite3 
sudo port install sqlite3
sudo port install apr-util
sudo port install openssl
sudo port install apache2 +preforkmpm

to separately install the dependencies (these were the ones that were 
coming up automatically when MacPorts tried to install apache2).  And my 
script now works without problems.  But my question is why?

1.   Why does one need the "sudo port clean sqlite3" command?   After 
removing the /opt/local directory,  why should any cleaning be needed?
2.   Why would breaking the script up into the separate commands above 
make a difference?

Thanks in advance,
Tom