The Plant Booster device reacts to the weight of the container it has been set to control to.
The device cannot distinguish between what weight is the plant, or the weight of the soil in the container. It only sees the sum of the two.
At the beginning of the season, when the plant is small, less weight is in the plant, and as it grows, more weight is in the plant. The Plant Booster will maintain the overall weight, so as the plant becomes heavier, the soil will start to become drier (and therefor lighter) to maintain the overall weight as the same. Normally you can expect this to happen very slowly, like over the spoace of a month or so.
On your regular rounds to tend to your plants, say once a week or so, trimming and dead-heading as necessary, and checking water will drip when the container becomes lighter (gently lift by hand), also check with your finger that the soil still feels moist. You will need to check deeper than the surface, say an inch or so or deeper, and decide whether you should adjust the Plant Booster device for a slightly heavier setting. Tighten the wingnut a quarter turn, and let the water drip in. It will stop dripping once the container has reached its new set weight. Then repeat the process some time later.
Some plants, due to their hardiness or tollerance for a fairly broad range of soil moisture content, may not need any adjustment troughout the season.