Why pilots deliberately pull back thrust seconds after lifting off the runway

How does this affect the aircraft as it takes off?
Autocar on MSN

Top 10: The best vertical take-off warplanes

Top 10: The Best Vertical Take-off Warplanes ...
Interesting Engineering on MSN

100% hydrogen-powered jet engine from Rolls-Royce reaches full power in landmark test

A major milestone in the race toward sustainable aviation has been achieved after a ...