You get an earlier harvest of larger fruits, although the total yield is often reduced. Many gardeners enjoy seeing how quickly they can get the first ripe tomato. These protective plastic shields can help by giving your plants an earlier start on the growing season. You can set plants out earlier because the Wall O'Waters shield the plants from cold temperatures. It's still helpful to warm the soil before planting by spreading clear plastic Reflective Red Mulch over the bed.
Consistent moisture is critical to growing good tomatoes.
Fruit cracking and blossom end rot can result when the soil dramatically alternates between wet and dry. Mulch helps, and so do these black plastic collars that are placed around young seedlings. They also warm the soil and create a barrier around the stems to foil cutworms that like to chew seedlings off at the soil level. Last year many of my tomatoes ripened unevenly, with one half red, the other green. Inside they were hard and green.