Assuming time is not an issue, is there any drawback to setting a large difference between the target and maximum bitrate, in order to save space, when using two-pass VBR? For example, if the original footage had a bitrate of 18 Mbps, and I set the maximum bitrate at 18 Mbps but leave the target at 10 (or 5) Mbps, would Premiere allocate just the right amount of bits for the footage, even if this number may actually be higher for most of the clip. I did read on this forum that VBR produces a lot of artifacts as the bits allocated can change frame by frame. Thank you.
I'm definitely not a compression engineer, but I've done a lot of exporting, especially lately, and I find Premiere Pro (and/or AME) perform best using 2-pass VBR with a low threshold (small difference between target and maximum).
To answer your question directly, yes, the point of a "Maximum Bitrate" is to allow the compression to rise above the target bitrate where needed, but my understanding is that the software is always trying to hit that "target bitrate". For this reason, I select a target bitrate which gives me the quality/file size I desire, then I set a maximum bitrate no more than 2-5 mbps above the target. My thinking here is that I don't want massive jumps, e.g. the target bitrate may be working great for a huge portion of your cut, but if certain parts require a higher bitrate, I don't want those to look significantly better or worse than the target bitrate portions. Thinking this way, I might as well use CBR, but what I'm really after is the "2-pass" portion of "2-pass VBR". If you are doing one-pass VBR, you might as well do CBR. If you need a fast/preview output, CBR. In all other cases, use "2-pass VBR" with a target bitrate as high as you can afford.
If you are really concerned with quality, find a 1-5 second portion of your edit with a lot of movement and/or color contrast, export just that section with a variety of encoding options, pick your favorite result and go on lunch for the final export.