A mixed number sits between two whole numbers
On the number line, 2 3/4 lives a quarter of the way between 2 and 3. That position is the everyday advantage of the form: you can see at a glance that the amount tops 2 but falls short of 3, which an improper fraction like 11/4 hides until you divide.
The fraction part is always proper — smaller than one whole. If the fraction part reaches or passes the denominator, as in 2 5/4, the writing is not a finished mixed number: 5/4 holds another whole, so the standard form regroups to 3 1/4.