CSS shorthands reset all the properties you’ve declared before. For example, when trying to center an element horizontally, you might use margin: 0 auto;, which actually is interpreted as:


margin-top: 0;
margin-right: auto;
margin-bottom: 0;
margin-left: auto;

In large projects you may accidentally override one of these properties, so you should better set only the properties that are necessary:


margin-right: auto;
margin-left: auto;

The same applies to properties like background, font, border etc.

It’s not like a rule of thumb, I even dare say that CSS shorthands are good, but try not to overuse them in relatively large projects.