The fraction 70⁄78 works out to 89.74% when you write it as a percentage.
Seeing it this way makes it easy to compare with other numbers, like test scores or discount rates. A value close to 90% shows that 70 is almost as large as 78.
In everyday situations you might use this percentage to estimate how much of a whole something represents, such as the portion of a project that’s finished or the share of votes a candidate received. It’s a quick, clear way to communicate the size of the part relative to the whole.