I noticed a lot of things that a person signs to make legally binding, have them write the date too. Why is it important to know the date a document is signed? Does it some how help prove something?
Dated signatures are not required to form a contract. However, it is evidence of when the person signed the contract and therefore agreed to be legally bound to it.
This aids in resolving disputes about whether or not the contract has commenced, although thorough drafters will also include the date that the terms of the contract are to commence (especially in employment law) as an explicit clause.
A person who purportedly breaches the contract has a defense if the purported breach occurs prior to their signing of the contract. A person who is seeking damages for breach of contract can use the date to prove that the person who has breached the contract was aware of and had agreed to be bound by (and perform their obligations under) the terms of the contract.