Hey! Play nice people!
What Akashio is asking is about the buffer, not the filesize. VBR mpeg requires more CPU power to playback than CBR because it's constantly looking ahead and altering the bitrate of the next image sequence accordingly. If the playback looks really blocky then your buffer isn't high enough so you can turn it up to improve clarity. However, doing so is much more demanding on the CPU.
When I encode, I use tmpgEnc (ver 2.56 'cuz it was the last version I paid for) and I set the VBV buffer size to "automatic". It does a REALLY good job of only putting in what it needs. Takes a little longer to encode, but I can do 320x240 CBR encoding in realtime from tmpgEnc so I really don't care about the little extra time. My other settings for VBR are max bitrate = 1500, min bitrate = 1. P and B picture spoilage are both set to 0. Why do I do this? Well the first two are easy to understand. I never want the bitrate to go above 1500, and the lower the bitrate can be the better, so I put in 1 (you could put 0 but when you think about that, something ain't right...). For the spoilage they're both at zero because what I'm telling tmpgEnc to "use the lowest possible bitrate to display this set of images perfectly, but don't go over 1500". So basically, if it needs the bitrate, it will go as high as 1500, however if it doesn't need it and can render the sequence without noticable loss of quality, it will use less bitrate. In my videos it usually shaves off a MB or 3 from if I used CBR 1500, but hey, every little bit helps!
As for the filter I was "experimenting with" that was "ghosting". I wasn't experimenting with it at all. It was just a filter that was open at the time. That's not REALLY me editing for this video. It was just something I staged (although I did dump it in to the actual project). In fact, you cant' see because the size of the clip, but the name of the clip I'm "editing" is "this clip doesn't exist.avi"

"With free bagels we can live like Kings!...Kings who have to pay for their own castle in order to get the free bagels!" - Omar Jenkins