Buying 2nd home and renting first

The point is that there's no security in long term leases. If a tenant wants to re-assign the lease and the landlord doesn't like/trust the people that the lease is being re-assigned to, then s/he has no comeback.
 
In fairness it is far more likely that the tenant will just leave or give a months notice than go to the trouble of finding someone to assign or sublet to. That would be well down my list of weaknesses

They could also die. Then you'd be stiffed for the rent.

Ho, ho.
 
Sub-letting and assigning a lease are two different things. If you assign the lease, you lose all obligations to the landlord and the assignee assumes those obligations.
 
In fairness it is far more likely that the tenant will just leave or give a months notice than go to the trouble of finding someone to assign or sublet to. That would be well down my list of weaknesses

I still think that if a tenant leaves a fixed term lease early and there is no break clause, then s/he could be held liable for the rent for the rest of the period.

Don't forget, a lease is still a contract (albeit a specific type of contract). A tenant is agreeing to pay a landlord x amount over y period. If there is no break clause, I really don't see why the tenant couldn't be held liable.