Hi and welcome to the forum
If I understood correctly, you noticed a reduction of the free space in your laptop HDD after using DVD Shrink, right? Or maybe you are referring to RAM memory?
If you are referring to the laptop HDD, then the most probable cause is that DVD Shrink creates some temporary files after analyzing the discs.
These files are located differently according to the operative system you are using.
On Windows XP these files are located in C:\Documents and Settings\All USers\Application Data\DVD Shrink.
On Windows Seven, these are located in C:\ProgramData\DVD Shrink
If you used DVD Shrink on a very large number of DVDs, this folder can contain a lot of data, and this explain why the HDD is filling so quickly