Oh of course it's nowhere near the actual number that will attend. But the RELATIVE numbers are interesting.
For example, on Friday, these panels have the following numbers of people 'interested' in them:
10:15 am TMNT 146
11 am Venture Brother 216
12:05 pm Big Bang Theory 949
12:30 pm Firefly 1301
1:25 pm Walking Dead 1061
1:45 pm Bones 475
2:45 pm Game of Thrones - 1142
3 pm Robot Chicken 302
3 pm Arrow 384
4:30 Falling Skies 306
5:30 Joss Whedon 607
If you compare these RELATIVE numbers against the room capacities, it allows you to see when some rooms might fill up faster or perhaps not even fill up at all. Also, it may help you make decisions on what to attend if you have conflicts.
I find it interesting that right now Firefly looks to be the most 'popular' panel, despite all of the hoopla going on in Hall H.