In addition, many people push harder when they are out of the saddle, making it "harder". But you don't have to. Do some drills concentrating on standing and going easier, and then you will detrain the standing = go harder response.
This advice is good. But for a given speed, climbing while out of the saddle is inherently less efficient than staying seated, because more muscles have to be recruited to generate similar power. So you should get out of the saddle either to accelerate or to vary the position/effort, but be aware that it has a cost in terms of energy expended.
Here's a link