Paint is basically used to decorate and protect surfaces. The surface may be the walls in your kitchen or bedroom, or a car, as examples. In your house, the most important function is to decorate, while for a car the most important function is to protect. The type of paint you would use in either case would be different, as would the paint manufacturer's choice of titanium dioxide grade.
Titanium dioxide is by far the most important pigment used in paints.
Both by definition and use, the importance of titanium dioxide in paint is apparent. As titanium dioxide pigment replaced less efficient white pigments, such as lead sulfate, lithopone and zinc oxide, the quality of paints increased. The improvements included one coat white or pastel shades and high gloss white latex paints. An equally important use of paints and coatings is to protect a surface. This is usually for paints that protect exterior surfaces, such as house siding, and automobile finishes.