May I offer a contrary view, and one which is based on dance as a social form, and not in respect of dancesport.
No one who does not regularly seek out and enjoy dancing with a variety of partners can really dance at all. Dance is, fundamentally, a social activity, and restricting yourself to one partner is basically anti-social, and also means that instead of becoming 'attuned' to the nuances of your partner's style of movement, you lose all abiity to dance with good technique, and to develop, properly, the lead and follow skills that would enable any first-rate dancer to dance with anyone - complete novices included.
Having a preferred partner (spouse, commonly) and being particularly 'at ease' when dancing with them is one of the great pleasures of dancing, but dancing at our best with a regular partner is the product of our experience and skill, not the foundation for it.