No. Not in the sense that you need food, water, and a good sunscreen. You need to get a yearly mole check. You need to stop picking at your nails. You don’t need a hair primer. But it might help.
Like other primers, hair primer isn’t an absolute necessity, but depending on how you style your hair every day, it could make a difference in keeping your ‘do done longer.
Do you blow-dry, curl, or flat-iron your hair every day?
If it does, then a primer might help. Prime Style Extender from Living Proof  contains an ingredient that protects hair against humidity—the #1 culprit that makes heat-styled hair go limp and lank. The company’s proprietary OFPMA molecule seals the hydrogen bonds that are created during heat styling, helping them to stand up to fluctuating weather—heat, humidity, etc.—resulting in a style that’s a bit more resilient. If your hair doesn’t frizz or go flat as quickly, you won’t need to shampoo it or touch up the style as often, and not only does that safe you time and energy, it also saves your hair from excessive washing and the damaging effects of heat styling. Even if you live in the most hair-friendly climate, a product that helps you style less often could be a very, very good thing.
Do you heat-style your hair for special occasions only?
If you occasionally blow-dry your hair for big meetings at work or use a curling iron once per month on date night, hair primer could help, but probably isn’t necessary. Primer can help styles last for days instead of hours, but if you only need a style to last for a few hours in the first place, then it might not matter.
However, even infrequent stylers might sometimes find a hair primer invaluable. For instance, if you’re planning on wearing an updo to a wedding in August, primer could help make sure it lasts without getting deflated by humidity. (That goes double if it’s your wedding.) If you’re planning a big work event that lasts all day, a primer could keep your style from falling limp after just a few hours of running around. If it unexpectedly rains on a day that you need to look your best, primer could be your lifeline. For the few times that you need your style to have super-human endurance, having a primer on hand could make life easier.
Do you primarily let your hair air-dry?
If your daily routine is more “wash-and-go,” a hair primer won’t make much of a difference in hair’s stylability or a style’s longevity. To get a boost in volume, try using a more lightweight conditioner or a styling product without silicones. To cut down on how frequency you need to wash, consider alternating real shampooings with days of using dry shampoo  to eliminate oil and dirt.