Compiling speed and output: includegraphics vs includepdf - what are the differences?

I made a .tex file and compiled it via pdfLatex in two scenarios:

1. (1200 pages long)

includegraphics*[scale=1]{example.pdf}

added some text here and there

newpage

(repeating this with example2.pdf, example3.pdf, example4.pdf etc.)

2. (1200 pages long)

includepdf[scale=1]{example.pdf}

added some text here and there

newpage

(repeating this with example2.pdf, example3.pdf, example4.pdf etc.)

In the firs scenario, the compiling took about 5 seconds (output ca. 650 kb).
In the second scenario, it took about 60 seconds (output ca. 373 kb).
(-> less size took more time)

My question is: why and what are the differences?

My goal is to print the 1200 page document with the best possible quality. Do one of the methods suffer from quality (like sharpness, color, overall, details etc.)?

Thanks a lot!