I understand that RAM may be wasted.  However, the issue I run into is that sometimes my crazy complicated 32bpc compositions will not render multiple frames simultaneously due to lack of available RAM.  I have to make an educated guess as to how much RAM each background process might need to render a given composition.

Fine tuning the memory settings to improve performance is one thing but in my case I'm trying to avoid falling back to a single foreground render process.  If there were a setting in the memory preferences that would allow AE to estimate memory usage for a given comp, apply a multiplier (say 1.2x) and then spawn the appropriate background processes based on this estimate I would avoid a good 20-30 minutes of headache every time I have to render one of my uber-complex comps.  I dare to dream :)

-D