In the event such a tenancy is created, such a document might go some way to establishing, retrospectively, what the parties agreed, if only the most important core terms.
As this is always post contract it has less value than a pre-signed tenancy which is always best practice.
On one occasion we arranged to meet a substitute tenant at a house to sign the tenancy agreement.
The tenant arrived late after the agent had departed and the fellow housemates allowed entry, whereupon he unpacked.
A subsequent phone call asking what time we might expect him to arrive resulted in him advising he was already resident.
Racing quickly to the house a signature was secured that day.
Had he refused to sign, the matter would have been more complicated.
He would have become a licensee of the original tenants and a potential civil dispute, might have ensued. Whilst in these circumstances the landlord would have won the case, it could have been time-consuming and costly. Now, we insist all contracts are signed in our office to minimise the risk of such a recurrence.
We also tightened up our contract to prohibit such fellow tenant access.