Another example for tenancy is that your landlord can not prohibit you from keeping small pets[0] (including cats) even if you sign it.
Another example is that EULAs are prohibited by law from containing any clauses that a customer could not reasonable be expected to assume to be in them. This hit WhatsApp when it tried to ban users who used unofficial clients (which would not violate the EULA of most other messaging services and can therefore not be prohibited simply by adding a clause to the EULA).
[0]: within reason, obviously. The landlord would have to prove that the pets present an unreasonable nuisance to your neighbours or cause unreasonable amounts of damage to the landlord's property.
Another example is that EULAs are prohibited by law from containing any clauses that a customer could not reasonable be expected to assume to be in them. This hit WhatsApp when it tried to ban users who used unofficial clients (which would not violate the EULA of most other messaging services and can therefore not be prohibited simply by adding a clause to the EULA).
[0]: within reason, obviously. The landlord would have to prove that the pets present an unreasonable nuisance to your neighbours or cause unreasonable amounts of damage to the landlord's property.