The pronoun that introduces a defining clause (also called an essential clause or a restrictive clause). A defining clause gives information essential to the meaning of the sentence. If you remove it, the meaning of your sentence changes.
Example: My model that uses Anaplan's new import capability is ready to view.
In this sentence, you understand that the customer has at least one other model. Specifically, the model they're talking about is distinguished from their other models because it uses the new import capability.
If you removed the clause that uses Anaplan's new import capability, you would lose the implication that the customer has more than one model, and even if you somehow knew about the other models, you wouldn’t know which one was using the new capability.
When possible, err on the side of defining clauses, as they generally make sentences shorter and easier to read.
The pronoun which introduces non-defining clauses. Unlike defining clauses, non-defining clauses (also called nonessential or nonrestrictive clauses) don’t limit the meaning of a sentence. You might lose interesting details if you remove them, but the meaning of your sentence will still be clear. Non-defining clauses are generally set off with commas.
Example: My model, which uses Anaplan's new import capability, is ready to view.
Here, the new import capability is simply a description of the customer's model. There’s no implication that the customer has built more than one model. You could remove the non-defining clause and the sentence would still make sense to a reader.