i use P6, so i manually adjust my max texture size to match my render.  P7+, my understanding is Firefly handles it and gives you only what you need. 

if you're making textures, the trick is to plan for what you'll probably need with some leeway for what you might need.  my final renders are at about 2700 x 3600 right now.  so if i want, for instance, to submit them to a book contest, the image is high enough resolution to print.  i'm not high enough res for a poster.  that would be about quadruple the area at just 200 dpi.  so if i could get Poser to render that large, i'd definitely need to max out the textures.  and what if i wanted a close-up portrait that size?  i'd need the face texture to be about as big as the poster itself. 

i've had the most trouble with scenery, actually.  very few scenery artists make textures efficient enough to render at a high resolution.  even without doing a close up, i've hit some serious limits.  i've had to switch to procedural textures at times.  which has made me even more thankful for bagginsbill's teachings and freebies.  they've enabled me to use content i  paid for.