Breakdown of La flexibilidad horaria es útil.
Questions & Answers about La flexibilidad horaria es útil.
Because flexibilidad is a feminine singular noun, so it takes the feminine singular definite article la.
In Spanish, abstract nouns are often used with the definite article when talking about a concept in a general way. So La flexibilidad horaria means something like schedule flexibility or flexible working hours as a general idea.
If you left out la, the sentence would usually sound incomplete in normal standard Spanish.