No they're no limit actually, I have the emu mophatt keys emulated to sf2, <- my secret weapon, and it takes up a half a cd, and the advantages\disadvantages are well the bigger it is more samples and more samples means more memory and cpu power, so the big sf2's are a hog on your digital lady, but bigger usually means better quality or as you asked earlier, someone just went and compressed a whole bunch of crappy ones together to make one really crappy big one, but technology doesn't sit still and loves to change, so in a short while you'll be hearing about megafonts- these are the mother of all soundfonts and can hold a whole keyboard in a tiny little file, so soon gone are the days of going to sam ash and buying a real keyboard all you'll soon need are just the keys, but its a whole new world i'll have to explain when they done working on the technology and it becomes standard, but just like digging in crates for em grimy records to sample, treat sf2's the same way- download/buy them and sift through for the treasures and what I usually do is re edit the samples and rearrange them like for example (sales pitch) the 7 cd set i'm selling i just combined three, four sometimes five crappy ones to make a banger, all you need is just a deep understanding of frequencies and such and these babies will come out sweet, if you listen to my tracks how they usually have those (different,weird ) type of sounds, its usually the soundfonts I have, they are re-invented to how I like them, my way .
Hope I helped
