[sliverstorm]

It really depends on what you are making. Blinking LED's require little theory, and voltage dividers never really need to be precise.

But, when making a multi-pole active filter, the whole "grab a few resistors and test it until it works" is a colossal waste of time- you need the graphs, equations, and so forth (or at least a computer program that will take care of that).

[bwarp]

You also need to build it still as at least 50% of the time, there are problems with the ideal world simulations.