There are many elements provided to support accommodation when both in service and afterwards (which may or may not be taken up by people, and in different ways)
The different services have different general styles on postings for the service person and their family, historically the navy would obviously go on ships, and the family either stayed in their home town or in accommodation in their main port. The RAF were fairly similar
The army would move a lot - with families opting to relocate to each garrison or in their home town
The army has refined the way that it works, building up larger garrisons with less small
locations, and aiming to keep types of capability in proximity making it easier to have a stable home life in service accommodation
Peoples lives have also changed with the spouse having their own careers and may take more of the home town option with the service person doing weekly commuting
People also have different priorities on a private home, some will just take up SFA and spend or save the money saved by using subsidised accommodation, others may invest in property and either use it for the family or rent if out. It might be their intended future home, or it might be an investment to sell on before buying their future home
This is further encouraged with schemes such as ‘help to buy’
Trials include giving the ‘subsidy’ to the service person for them to choose their own accommodation instead of SFA
If you use SFA you are charged an amount of rent, but that is well below market rate. The subsidy is deemed to be the difference, but is also a hidden cost in managing the SFA - so an amount of money would be saved by not providing SFA.
Most of the SFA estate was sold to raise capital to restore standard after a lack of investment
This was the Annington Homes contract - the properties were sold and rented back. The government retained landlord maintenance responsibility, (and had sold at a price assuming the properties were up to standard - whxib they were not - the theory being that the capital raised would be spent on improving. If the MoD no longer required the properties they were handed to Annington (and probably paid a penalty for the lesser condition) but did not then pay rent and Annington would put them to development or sale etc
The Annington under market rent and maintenance costs are the subsidy that could be saved by not using SFA
(and there would not be a need for MoD to pay full market rent for a substitute house that they get a discounted rent back from the family - just give an allowance for them to choose a property to rent or buy