Just as in any relationship, we should heed both, said Stacy London, author, co-founder of Style for Hire and co-host of TLC's "What Not to Wear."
"The big thing is you need to be able to identify between the two," she said. "Any item in your wardrobe should satisfy one of two criteria: utility and joy."
A need is something that will be used frequently and will outlast a trend. Applying a cost-per-wear metric, spend more for the best quality you can afford, London advises.
A want is something you want, period, for whatever reason. "And you're allowed," she said. Just recognize that if it's trendy, you should spend less. "Forever 21 is my favorite place to buy costume jewelry. For $7.90, I can get amazing chandelier earrings that if I wear them five times will have been worth the price."
The reason so many people have a dysfunctional relationship with their closet is that wants drown out needs, or vice versa.
"If you only have work clothes — the black trouser and ribbed turtleneck you got four years ago at the Gap — you're not participating in your own style personality," London said.
Conversely, you know you've amassed a wardrobe of wants if you love each piece, but nothing goes with anything else.
Picture a closet as a pie chart, with roughly one quarter each devoted to neutrals/solids, brights, prints and evening/sparkle, London said.
"Chances are that's going to give you the right balance of things to play with. I don't feel you have to have skirts and suits and pants and dresses; that depends on the woman and what she feels is more appropriate for her. But if you're looking at basics, neutral pants don't have to be boring black polyester. Look for a cut that has a great detail, like a top stitch or a tuxedo stripe. If you give yourself permission to find the interest or whimsy, even in the basic, even the needs will deliver satisfaction."
"You need a trench coat, but you also want to look cute, because you might not take it off when you go inside," he said.
His target is fashion-savvy women in their late 20s or 30s who have outgrown trendy clothing but aren't at the luxury tier.
"They're looking to pieces that they want and also that they need," Wu said. "A good collection should fulfill both."
Jennifer L. Scott, author of "Lessons from Madame Chic: 20 Stylish Secrets I Learned While Living in Paris," advocates cleaning out the closet and establishing a capsule wardrobe of 10 items each season.
"Most women have way too many clothes," Scott said. "It's confusing us when we need to pick something to wear. It's clouding our judgment as to what our true style is. The problem is there are too many wants in our closets."
The French women whose style she admired had capsule wardrobes. Accessories, which don't count toward the capsule, were often where wants entered in.
"They wore the same things all the time, but what they had were high-quality pieces that really spoke to their true style. They didn't have a schizophrenic wardrobe. What a lot of women have to get over is that reluctance to wear their best on a daily basis. The capsule wardrobe forces you to wear your nice silk blouse to the grocery store instead of only to lunch with a girlfriend."
That's the genius of the capsule wardrobe, she said. A busy woman will always look good.
In a society that loves to shop, Scott advises pausing a few days before purchasing and asking, "Does this contribute to my wardrobe or is it just going to be clutter?" Even with this discipline, she has more fun shopping now.
"The old way of constantly shopping, it produced a lot of guilt. There was all this neurosis attached to it."
Now, before each season, Scott reviews what she has that still works and decides what she needs or wants to replace.
"Rather than randomly shopping here and there, it's really cool to sit down and say, 'What colors am I looking for this spring?' I might buy a mint-colored blouse and white jeans this spring, because my old pair is looking kind of scruffy."
A final note from London: She sees women denying themselves higher-quality needs as well as fun wants because of body insecurities.
"Style is not a reward for the skinny," London said recently on "What Not to Wear," which lit up Twitter. "It's not if I'm rich, thin and young. You may not like your size, but then don't invest in leather leggings. Let yourself want the expensive bag and really love it and show it off and have a ball with it. Style is joyful if you allow yourself to have joy."