partitioning - opt & etc

Okay, so new thread! As I was repartitioning my hard drive, I was trying to find out the lowdown on this /opt folder. This is a new thing since I have started running Trinity; I never noticed it before when running Kubuntu. Only after I started running the Trinity desktop, that is when I noticed the installation to /opt; and only then I noticed that other programs were installing in that folder. A friend told me that he creates separate partitions for both /opt and /etc; and then, too, I noticed that the new Icecat browser does something even weirder, which is to install in /usr/lib/icecat, rather than (like other Mozilla browsers) in /home/<USER>/.mozilla/. My question is really more or less the same for all these items. I want to be able, once I have configured them as I wish, just to clone that directory, so that I don't have to keep reinventing the wheel, over and over again. When I tried to research the /opt folder, I didn't find out much. If I create a separate partition, will I be able to leave it untouched like my home folder? Will Trinity (and other programs) automatically be installed there? I suppose could just back it up regularly, then overwrite it once I have reinstalled, but I would like to treat it like my /home/<USER>/ folder, and leave it intact. The same with Icecat: it seems to run better than Firefox/Iceweasel, but to install everything in /usr/lib/icecat seems very irregular. Is there some way to get it to install elsewhere? for example, in /opt? Bill