systemback as a performing tool ?

Today i performed Systemback to copy a system into a different partition in order to maintain an old Ubuntu 10.04 LL, I still, rarely use, but want to keep for the stability and the deep personalization I made along the years.

The space taken in the original partition of the system, ran on ssd (previously cleaned by UbuntuTweak) was 19 GB and I expected the same in the destination partition.

I was surprized the new space taken was 7.6 GB without user data file, and 11.7 GB with the user data file (Gnome monitor system results).
In the first instance, some nomatter file/directory, on the desktop and /home/user were kept too.
In the second instance, apparently the system is the perfect copy of the source, as it has to be and finally, the system run quite more fast and quick too, at least by an eye look.

So I would ask if this behavior is full trusting, and this use could be suggested regularly for improving performance?
I used "system copy", can I expect the same behavior for "system restore" too? I used 0.7.7.501_01.08.2014-gtk+

Many times I ran Systemback for live system and iso for redistribute Ubuntu 12.04-14.04 with great satisfaction.
Hope not to be to much --v (verbose), want to thank for this wonderful software.