When to use percentage?
Use percentage prior to embed images into documents
Let's compare a document containing a resized image with a document containing an original image.
We take an original image taken with a 16MP digital camera. Then we integrate it in a document once as original and once resized at 25% percent.
Let's look at the difference
We open both document with a zoom factor of 100% and look at a detail in the picture on the screen
Document with the original image
Document with the resized image
You don't see any difference? We don't see it either.
For the viewer, the quality is absolutely the same on screen and hardly noticeable on printed document.
The size is 16 times smaller, resulting in 16 times faster email sending and receiving, 16 times faster coping on USB stick and 16 times faster load from web.
Resize your digital camera picture to 20% - 30% of the original size prior to embed them into documents.