When LaTeX sees a period followed by a space, “. “, it assumes that the period is the end of a sentence, so it makes the space wider. When using a period that is not at the end of a sentence, the following space should be typeset using “\ “ instead of a normal space “ “. This ensures size of the space after the dot is correct.

Correct Incorrect 
My name is P.\ Wintz
$$\text{My name is P.}\ \text{Wintz}$$ 
My name is P. Wintz
$$\text{My name is P. Wintz}$$

The difference is subtle and the actual spacing will depend on the settings for a particular document, but the difference helps readers discern whether a period ends a sentence.