Rental agreements vary from an oral agreement to pay rent for a place to live indeterminately, up to multiple pages of "terms and conditions", including rules and obligations upon the tenants.
For the most part, written leases (often for a year or more) are to the advantage of the tenants because they may keep the landlord from arbitrarily raising the rent or throwing out tenants. The tenant, of course, may vacate at any time (it's not a prison sentence), knowing that some landlords may attempt to collect "damages" arising from a tenant's early termination.
If the landlord wants to place restrictions upon the tenants, beyond what is already in the pertinent laws, the "lease" is typically where they must do it. Things like prohibiting pets or sublets or tenants parking in the driveway, or perhaps late-payment penalties, are often laid out in the lease.
Just remember: it's a contract WITH a property right. If the tenant doesn't like the terms, they may either attempt to negotiate or walk away and try to find a more reasonable landlord.