On the whole a canard does not lead to greater efficiency. However its aerodymanics are complex and little about it is obvious. Pretty much any statement can be - and often is - contested.
Yes a canard will be used to lift the nose during takeoff, helping the main wing instead of adding to its load. Since liftoff is the highest-loaded yet slowest-moving moment in the flight, this does genuinely help wing loading and therefore size and weight, making the airframe overall more efficient.
But in a basic arrangement, for a plane to be stable the forward surface must be loaded more heavily than the rear. On a canard the main wing is therefore loaded below its maximum capacity, which means that it must be oversize and much or all of the above saving is lost. On a tailless type, the wing must similarly be made overlarge so that the rear surfaces can act as the tail (through either reverse camber or, if swept, tip washout). On the other hand of course, both canard and tailless avoid the need for a long empennage hanging out the back.
Fitting a high-lift canard so that the wing can work harder after all leads to safety issues such as the wing stalling and dropping while the canard still holds the nose up, and suchlike. It has generally proved too unsafe to put into production.
The canard's downwash will also tend to mess up the oncoming airflow for the wing, and that mess changes under different flight conditions such as speed and angle of attack, so the wing must have a good safety margin to tolerate such disturbances. That means more inefficiency.
However canards can provide performance efficiencies at high angles of attack by helping to manage the airflow over the main wing, in say a dogfight or when taking off and landing.
In most situations a canard works out more trouble than it is worth, either inefficient or dangerous. But there are exceptions.
The first two successful man-powered aircraft, the Gossamer Albatross which won the Kramer prize and the Gossamer Condor which crossed the English Channel, were both canards. Interference with the wing was much reduced by the low Reynolds number of the canard at its very slow cruising speed. It was also set physically lower, so that the wing passed over rather than through its downwash. So just because the canard is not worth it for sailplanes does not mean that it is inherently inefficient for all low-speed applications.
Several later variants and local modifications of the classic Dassault Mirage III tailless delta fighter were noticeably improved by adding canards. Although less efficient in cruise, at high AoA the canard improved the airflow over the wing to generate extra lift which outweighed the extra drag, improving its efficiency under such conditions. This made it more efficient in a fight for example, with the extra lift allowing the plane to hold altitude better during a tight turn.
Ultimately, if canards were less efficient when and where it really matters, they would not have been chosen for so many 4G/5G combat aircraft, such as the Eurofighter Typhoon, Dassault Rafale and Saab Gripen.
