Should I backup .odex files too?

I have recently got an app that permits me to view the contents of my phone memory on my rooted Samsung Galaxy Y mobile phone. In /system/app folder, I see all the system apps that came pre-installed with the phone, and also I see a .odex corresponding to every .apk file. What exactly are these files? I wanted to keep a backup of all these .apk files in my laptop, just in case. Should I backup the .odex files too? Why or Why not?