Public opinion on this question is mixed. Some couples think two sinks, two vanities, etc.

master bath

Photo by Life Begins At Thirty, Right?

are a complete waste. Others, however, insist on them. In fact, some large bathrooms are designed to have essentially two dressing rooms attached to a shared toilet/tub/shower area. If you anticipate selling your home in the near future, it might be worth designing for and installing two sinks. Most new homes are built with two sinks in the master bath. If the bathroom is small, you probably will not want to make it look any smaller by installing two sinks (if, that is, you could even fit two into the room).

Of course with two sinks come extra costs and work.  The sink itself and the faucet can cost from a few dollars to a thousand or more.  Then there is the cost of the additional plumbing.  With the counter space the second sink takes up there is usually a strong desire to add more counter space which means even more costs.  With more counter space there is often a trade off of storage since you may be giving up a closet or floor to ceiling cabinet.

As with everything there are trade offs with bathroom design but the end of the day, if you are inclined to get a second sink during your bathroom remodel then go ahead and do it because it is typically the best solution.