It certainly is not the only way to draw, but mostly it is to get you thinking about how everything relates to everything else. The more you draw the easier it will become to see the relationships between things and the "measurements" will come naturally.
"Complacency is the womb of mediocrity. " -- Jason Manley
"If you always put limits on everything you do, physical or anything else, it will spread into your work and into your life. There are no limits. There are only plateaus, and you must not stay there, you must go beyond them." -- Bruce Lee
I start with the longest axis and then establish that length on my canvas in the place I want it. This may or may not be the way it is in the real world. Once I establish that, I compare all other measurements to that first one so they are proportional. Then I check negative spaces and positive spaces and all angles starting with the biggest shapes and working down to the smaller ones.
I work pretty much the same way as dpaint describes - pretty standard approach. I also tend to check where line things up vertically above each other and horizontally across from each other.
As far as the actual measuring - it helps to be standing - arms distance from your work you have to measure from that same position/spot always - with arm extended and elbow locked. Also helps to close one eye and keep your work shifted just to the right or left of the subject - the less translation the better. Then it is a simple ratio translation from what you are measuring to your drawing.
The book "Drawing Essentials" by Deborah Rockman does a great job demonstrating the process.
What would Caravaggio do?