Very young tomato plants will at times flower prematurely, they’re rearing to get going and growing. Some gardeners pinch off the first flowers of spring on tomato plants, particularly just prior to transplanting into soil.
It’s not absolutely necessary but it does make for a stronger plant. For starters the chances of very early flowers being pollinated are slim as there are not very many bees or butterflies buzzing around just yet. Pinching off early flowers from tomato plants also enables the plant to establish a stronger root system for accessing soil nutrients, as well as healthy foliage essential for synthesizing sunlight.
Once the tomato plant is established there are other types of pinching back that are helpful. See: Pruning Tomato Plants