From TRAC's Tenant Survival Guide:
The Residential Tenancy Act requires that your landlord provide you with a written tenancy agreement. The reason for this is that when an agreement is written, you have proof of what you and your landlord agreed to. This proof an come in handy if you ave problems later on. Tenancy agreements tend to protect landlord’s interests, but may not protect yours. Before signing make sure you can live with the terms of the agreement.