Targa is usually an uncompressed format and can be of a deep bit depth. When you export targa images from a video sequence, the NLE will uncompress the video stream and export each individual frame in its entirety as a standalone image. Each image is not recompressed. So it becomes very much like film in that you have discreet images for each frame of the video.If you look at the file size of all the Targa images you will see they are exactly the same because they contain the exact info to reproduce each pixel.
One thing to note, is that although the Targa images are uncompressed, you are still limited by the information in the original video file. So the compression artifacts will still be there. BUT, and here is the key, you have not introduced any NEW compression issues by using targa images. So you can hand off the Targa images to someone else, for effects or whatever is needed, without fear of losing quality when exporting from your NLE. They can do their work and in turn export Targa for you and similarly no quality will be lost (except, of course, any quality loss from the work they did on the footage). Its an excellent way to collaborate over footage.
Couple caveats, your video files (sets of stills) will be large. So you will need the storage to move them around OR a lot of time to ftp them to the other person. You need to make sure the person receiving the images can pull in a sequence of stills as a video file into their NLE or effects program (most if not all can). You need to make sure the images are numbered sequentially at the end of the file names so that the NLE knows how to order them (most if not all NLEs do this for you automatically when exporting Targa, though you need to make sure the name has the numbers at the end). Finally, and this is very important, make sure to use the exact same frame rate when exporting and importing, otherwise frame blending will occur to match the frame rates OR your footage will play back too fast or too slow in the receiving NLE.