Say for example you have a product page, and you wish to have 3 images of the product. You can create a field call images, and have a list of all the sources of the images, e.g. image1.jpg, image2.jpg, image3.jpg. Then you can create an array for your images and run a loop to display them.
Alternatively you can create a new table called images, that can match the product up with the images, e.g. Product ID Image 1 image1.jpg 1 image2.jpg 1 image3.jpg
As far as I can tell you're asking if normalizing your database is a good thing ? Sure it's a good thing, it's the essence of being for relational databases.
So yes: separate tables and relations is by far the superior long term choice. Messing with creating structure yourself inside a field means the database can't help you anymore in the long run.
Just imagine in both cases what happens when you need a separate caption for each image, store the dimensions of the pictures, track the source where you got the picture, copyright status of each image, ...
You need to see a database as much more than a stupid table that holds data in a persistent manner.