The procedures implemented to support all weather ops vary hugely across the world. In the UK and many other parts of Europe the view is generally taken that declaring 'LVPs in force' tells pilots that it's safe to make a Cat II/III appraoch (assuming such procedures are published). But the procedures applied at the airport do far more than protect the ILS sensitive areas.
The actual procedures will often vary depending on the visibility on the ground or from the tower. Essentially, as the ground visibility falls more and more restrictions on ground activities are permitted, the intention being to prevent a variety of hazards to aircraft operations.
For example, one of the first things that usually happens is that contractors (i.e. those less familar with the airport or airside procedures) working on the manoeuvring area will be withdrawn - largely to stop them getting lost and going onto the runway.
When the visibility from the tower is limited restrictions are put in place to overcome the fact that the controller cannot see where the aircraft are. When the visibility gets so bad that the pilots are unlikely to be able follow instructions to follow the ABC A320 or whatever, further restrictions are put in place.
In the old days there were some fairly draconian restrictions that were implemented as soon as the weather reached certain criteria. This was not very flexible and often invoked unjustified limitations - I can recall days when there was some cloud (BKN I think) at around 200ft and 50 KM visibility below it.....and contractors had to stop work, almost no vehicles were allowed on taxiways, and so on.
Nowdays LVPs can be tailored to the operations at the airport and only protect whatever needs to be protected for safe ops in the prevailing conditions. But the principle that 'LVPs in force' means that the ILS is protected for Cat II/III ops remains.
It's not a perfect situation. There have been some incidents where misunderstandings about what is protected or what type of operation is permitted in LVPs. The one which sticks in my mind - or, at least, vestiges of it stick in my mind - is a Speedbird B737 (or maybe a B757) at Manchester which suffered a substantial uncommanded roll at 200ft or so during a Cat II approach because the ILS sensitive area was not protected.
As for LVPs for departure, that just means that measures to protect the runway from incursions and other things deemed necessary for movements on the ground are in place. For similar reasons you'll find LVPs at airports with only Cat I approaches or, somestimes, no precision approach at all.