Well, in my experience of the rental sector (in a smallish city), rentals are mainly taken up with young people who do not wish to take up longer term tenancies for a variety of reasons. Some need to move around for work. Others are filling a gap whilst waiting to buy. Others may be students for whom being in a,particular location is a temporary state of affairs. These type of renters seem fairly typical around here atm.
In the case of, say, families with children who need to be close to a school/ in a catchment area for a long period of time then security of tenure over the longer term may be more of an issue. Many landlords will not take people on HB and others who will not take children or pets, for example.
I must admit I can't think of any circumstances in which a tenant would vacate a property and then return to it within the period of the tenancy whist not having paid the rent. I've heard of landlords letting to the same student over the course of more than one academic year (with a break between them) but these would be under separate tenancy agreements. These properties would otherwise remain empty over the summer, so this arrangement works well for both landlord and tenant.
Would I allow a rent-free period in a tenancy? Truthfully, no. I think it's too much of an ask for most landlords, particularly small ones who depend on the income. Unless, of course, the missing rental period was somehow covered in another way (such as a higher rent for the rest of the period maybe?). Maybe such an arrangement would be workable in areas where there is a glut of property. I dunno. It's basically about what the market will stand. Supply and demand again!
You've raised an interesting point though. I think, as a nation, we have perhaps become overinvested in property ownership over the past fifty or sixty years. Ownership has peaked and has fallen back. What everyone seems to agree on, though, is that we desperately need more affordable housing.