Why should I sign anything with a real estate agent?

When you contact a real estate office, or an individual real estate agent/broker you will be dealing with someone who works on commission. These people (myself included) don't receive any kind of payment for simply working with people to help them buy or sell property. The only way they actually will get paid is for the the buyer/seller to commit to working with that individual or brokerage and eventually completing a buy or sale of a property. This is formal commitment is done (in Ontario) through a Listing Agreement (for a seller) or a Buyer Representation Agreement (for a buyer) --- many agents will insist on having one of these documents signed before spending any quantity of time with potential clients -- because there is no guarantee of any type of remuneration for their time, efforts and expertise without it.
Realtors can spend many hours, days, sometimes YEARS without seeing any actual pay from their time and efforts with a particular person. The old expressions: "there is no free ride" or "there's nothing free in this world" are not true with an unsigned consumer receiving real estate services. --- often the agent is working, with a reasonable hope and expectation that their efforts will pay off at some point-- but sometimes there is no pay-off, and the person doesn't make a purchase/sale -- or decides to work with someone else. Real estate is truly a high-risk business for the agents/brokerages.  It is reasonable for you (as a consumer) to ask a realtor/real estate agent HOW they get paid, and if there's something you will be expected to sign in order to have their help. Un-signed consumers don't usually get the same amount of time and attention as signed clients do.--- for the reasons explained above.