Blueprints are vital for a number of reasons. The most important, in my opinion, is so everyone is on the same page. Normally there would be several copies reproduced and distributed to the various entities involved in the building of the structure, tool, vehicle, etc. Blue prints are also important as a form of evidence should a mistake occur and someone is to blame. An example might be the laying of concrete. The concrete may need to be poured and allowed to dry in certain regions when the outside temperature is between 40 degrees and 90 degrees. If the foundation cracks later and litigation is an issue, those involved can go back and see what the temperature was on the day the concrete was poured. Then they can check the blueprints to see if this specification was listed in the plans. It may be an oversight by the architect or by the contractor.
Blue prints are facsimiles of the original drawing that has been prepared by an architect The relevance was more in the times , when drawings were drawn by hand, so as to get multiple copies (as a Xerox machine would do).
In the present context with modern tools and equipment there is not much need of getting blueprints of a drawing. But maybe some old department asks for it as they not revised their rule books. Still you can ask them if in place of blueprints, printouts of plans in triplicate or as per requirement would be acceptable.
It's a fading trend, not of much importance these days in most of the cities.
Nowadays AutoCAD is the best alternative for blueprints where in you can edit the plan and create multiple copies and changes.