"Blueprinting" is especially critical in class racing, like Stock & Super Stock where the idea is to optimize efficiency within the rules. Published NHRA/IHRA specs show minimums and maximums for just about everything. What you get from the factory is usually WAY off, resulting in less cam lift, less compression, etc. which means less HP. Having specs as close as possible to the published numbers as well as having them as equal as possible between things like chamber size, deck clearance, valve lift, piston & rod weights etc. will increase performance.
A few examples:
A valve spring with a little less spring pressure than the rest could cause the start of valve float in one cylinder.
The imbalance of slightly heavier piston or rod can cause a drag on the rest of the assembly. It won't be rotating as smoothly, like an out-of-balance tire, just not as extreme.
An intake valve with a slightly sunken valve job can hurt the air flow into that particular cylinder.
Ring gaps in one cylinder that are a little too tight can cause butting, drag and inefficient sealing in that particular cylinder. Too wide a gap can affect sealing, but it's not as problematic as too little gap.
A head chamber that is bigger than spec and the rest of them will produce less compression in that cylinder.
Cam lift is often lost due to production tolerances and bad valve train geometry. An OEM engine with an advertised .462" lift on the intake valve will be measure quite a bit less. OEM rockers actually check less than 1.5 and some lift is lost through the different angles of travel between the small block Mopar lifters and pushrods. So Stock class racers with a cam lift limit look for aftermarket rockers with closer to 1.5 ratios, some can be "corrected", like 273/ductile iron rockers, and any remaining differences made up with a cam ground having slightly more than the spec rule, as long as the end result is not more than the spec lift using a 1.5 or less rocker ratio. (There have been racers caught with proper lift, but using higher ratio rockers! A no-no under the rules.)
Some racers even flow many cylinder heads to find two that have ports that flow as close as possible to each other. Due to production tolerences and core shift, there are differences between heads as well as within the same head.
Get everything as equal and balanced as possible, and the engine will be more efficient. How much time and money do you want to spend to get things as close as possible?
I probably missed some stuff, but hope you get the idea.
There are no stupid questions. How else you gonna learn?
