the standard definition, VOB format files, recording to the DVDs that are playable in a regular DVD player can have a "limitation".
On many blank DVDs, you will see "120 minutes" (single layer blanks) or "240 minutes" (double layer blanks) printed. This represents the *maximum* amount of standard def, VOB file video that can theoretically fit on the blank DVD. "Theoretically" because there are some limitations related to your needs...
For instance, if you use a DVD authoring utility to create a menu, have background graphics or video or audio with the menu, that uses space and reduces the 120 minutes or 240 minutes to something less. Also, using ALL the space available on the blank disc is not typical because file sizes vary and how you choose to pack things on the disc will result in unused space. This is not good or bad - it just is. And blank DVDs are inexpensive, so this is not a big deal...
There is the case of what is exactly in your camcorder. At this point, all we know is that you have a consumer camcorder with a 80 gig internal drive. What we don't know is how much of that 80 gig internal drive is used and how much time we need to deal with from that recorded video.
Since we don't know which camcorder, we get to pick one. The Sony HDR-SR7 has a 60 gig internal hard drive. According to its manual, it can store up to
8 hours in its highest quality high definition mode
almost 23 hours in is lowest quality high definition mode.
This means the range of regular discs for video storage of VOB format files when "completely used" and no consideration for menuing or dividing up by topic or anything else to actually make them "useful" can be
8 hours... 4 or more single layer discs; 2 double layer discs
23 hours... 12 or more single layer discs; 6 double layer discs
I understand your camcorder has an 80 gig internal drive - use of this 60 gig is merely for example/illustration only. Refer to your camcorder's manual for record times on your camcorder using the video quality you selected.
*Most* of the discs I burn are edited video and of a single topic, only. Many of them have only 3-7 minutes of video on them. This makes finding a particular project easier.
And just to re-ask the question... If we assume your process is to get the video from the camcorder to the computer - or at least onto standard def, VOB file, standard def, regular DVD player usable discs, is it safe to assume that you will then be deleting the high definition files off the camcorder - so you can use it to capture more video. Now, lets fast-forward 5 years. How are you planning to watch any high definition video? It was deleted off the camcorder; the discs you made are standard definition. And you got a high definition camcorder because?