Colin's answer, while correct, is very short.
Queries do everything (well... almost everything) that tables do, PLUS because of field selectivity, formula inclusion, JOIN capability, UNION capability, and Summation ability, they do more.
You should learn more about queries as a way to get exactly what you want where you want it when you want it. BUT also to recompute anything for which a formula exists. (Your price formula, e.g.) You NEVER store that which you can calculate on the fly. Your computer is fast enough to transparently do this computation every time and thereby SAVE SPACE.
OK, you say, my piddly little MDB file is less than 100 Kb on its worst day. My hard drive has 200 Gb total space and is still about 85% free. So what space do I need to save? Why, internal Access record space of course. By not storing data you can recompute on-the-fly, you make your records shorter. BUT shorter records means faster operation 'cause the speed of Access depends on the number of records that fit in a fixed-size buffer. Shorter records in fixed holder = more records in that holder. Which means faster, more efficient operations.
Colin told you the "what" of the issue. I just told you the "why."
