1- 4weeks off is not deconditioning
I read a lot of people mentioning time off from PE as " deconditioning". Let me first say that not taking a break from PE is one of the worst things you can do for long term gains and this has already been established by the community.
What people are hoping to accomplish is to restore the elastic and deformation potential of the tissues and think by taking 1-4 weeks off they are achieving this because they are able to continue to make continued progress at a rate which was potentially faster then immediately proceeding. In order for tissues to actually " decondition" and undergo scar remodeling, tissue conversion and neovascularization this takes months and at times a year or more depending on the extent.
The purpose of the 1-4 weeks off is to decrease the inflammatory responses and corresponding tissue/ligamentous edema. After low grade sprains I see this on MRI persisting for weeks to months. By allowing this edema to subside and tissues to repair you are making it more elastic again and creating an environment conducive to new tissue generation and thus continued gains. You are also allowing new cells to form and thus have more tissue to allow continued stretching.
When you have chronic ligamentous sprains there is ligament thickening which one could expect to see persist for years after the trauma. The good news is that once the ligaments reach that length due to that chronic sprain they often to not usually shorten but do remodel and get thinner over time in absence of continued trauma.
In summary 1-4 weeks breaks are recovery periods to help optimize continued gains. True deconditioning will often take a year plus if you are at the point that scar formation is limiting further progress. When one needs these breaks depends on the intensity of training and how well they are recovering. I personally take 1-2 weeks off per 8 week training cycle.