The movement of clothes, the dressing/undressing activities, and circulation through the space are important determinants of the location of clothes storage in relation to other parts of the bathroom. There are other factors to consider as well.
Moisture is produced in the bathroom, and excess humidity can be damaging to stored clothes. The clothes storage area should be separated from damp areas of the bathroom by a door or partition. Good ventilation in the closet area reduces moisture problems and helps keep clothes fresher.
Consider what is on the other side of the closet wall. A closet on an interior wall can be used to advantage by providing sound insulation. For example, a bedroom closet can reduce sound transmission from other parts of the house, keeping peace among late-night television watchers, early risers, and late sleepers in the household.
If the closet will be on an outside wall, it is important to determine that the wall is well insulated. The clothes in the closet will act as insulation from the room air, and the closet could be cooler in winter and warmer in summer. This could lead to condensation problems and even mildew on clothes. Ventilation and air circulation will be especially important to prevent these problems.