lol. meters aren't going to increase yield by themselves. They are tools. Nothing more. Does a trowel increase your yield? At the same time do gardener not need something to dig dirt with? Does a jug for water increase your yield, or is it just a tool to make your job easier?
Anyway. TDS meters are usually used for two things. As mentioned, it allows you to accurately determine the concentration of nutrients in solution. More common for hydro, but works just the same for the water going into soil as well. The other place I use mine is on my RO/DI unit, to ensure that the water I am getting out of it is pure, and to help me gauge when the membranes need to be changed. I grow in soil, not hydro. You are simply not thinking about it the right way. It's not a new fangled gadget claiming to "give you lbs!". It's just a simple tool to determine how pure water is, or conversely, how much of a substance you have added to water.