I have little experience at making dvd backups to my movie collection so pardon me for asking - but what do you mean by compression?
With Clonecd the size of the original disc must equal the size of your blank disc.
So if you have an original disc with two layers (dvd-9, 8.5 GB original movie disc), your blank disc must also be 8.5 GB if you use Clonecd.
Some movies are on single layer discs (Rob Roy Region 1, for example, is a single layer dvd); for those, you can use regular single layer blanks with Clonecd. But most movies (The Lord of the Rings, etc.) are on two layer discs (dvd-9).
If you use dvd-5 (4.7 GB) blank then in order to fit the material from most original discs (which are twice the size, basically), the video material must be compressed. Clonedvd can compress. When you compress video material, the picture quality decreases. Consequently, I hate compression. I am very picky. I don't compress. Clonedvd is also a transcoder. Transcoder compression quality is inferior to encoder compression quality (example of using an encoder is Dvd Rebuilder with Procoder or CCE). Encoders take quite a bit longer than transcoders to compress video. I hate compression altogether. I hate reduced picture quality, and I also hate taking forever to use an encoder to get good picture quality.
The drawback is Verbatim+R Double Layer blank media is not cheap (nor is MAM-A +R DL blank media). These are the only double layer blank media choices anyone should be making.
Most people are not like me. Most people use single layer blanks because the blanks are significantly cheaper than double layer blanks. So most people use Clonedvd, DVDShrink, or Nero Recode (these are transcoders). Some people don't like the picture quality these programs produce. So they use dvd rebuilder with a freeware encoder, typically HC Encoder (which is very good). But encoders can take hours to compress video (a very long time).
Again, I use Clonecd with Anydvd running in the background and Verbatim +R DL blank media (made is Singapore . . . much of it is now made in India; and it's not quite as good as the stuff made in Singapore). MAM-A +R DL (8x) is a good second choice. I am lazy; I prefer not to compress video; I prefer to retain the original layer break position; I prefer to also backup any PC files that may appear on the original disc. But I do pay more for blank media.