I was confused too but the article was helpful:
"This is a step in the right direction for MLS but it’s not all the way there, yet. As such, it’s important to understand how much we can use these new data points when we discuss MLS teams, roster building and salary cap dynamics. If we think of MLS rosters as a Wheel of Fortune answer, we’ve just filled in R, S, T, L, N and E. For some teams, if we buy the right vowel or guess the right letter, that might be enough to solve the puzzle. For others, we’ll still be a bit off from being able to solve."
"Now, at least, we have player classifications (TAM, DP, U22, homegrown); the number of guaranteed years in a contract (which helps with budget calculations and also factors into trade value) and option years; we also know how much GAM each team has to play with.
We can at least start to play around with what roster flexibility teams might have."
As a side note it's annoying that nytimes doesn't let me use my gift links for athletic articles.