Previsibines is a slang term for previs/precombines which are a couple of ways that the game improves performance.

PRP refers to Previsibines Repair Pack (PRP) Stable Branch. This mod contains 2 plugins, PPF. esm which contains a ton of bug fixes, and PRP.esp which regenerates previsibines since PPF.esm breaks them.

Precombines: Everything in the game is made from a mesh. Precombined meshes are a bunch of meshes merged into one, so instead of 10 meshes getting loaded only one does, which improves performance. If a mod changes any of the items placed in the world (also know as a reference) which has a mesh that are part of precombines, then it will "break precombines". And now the game has to load those 10 meshes instead of just the one. To determine if a reference is part of a precombined mesh, open the plugin in FO4Edit and check for brackets around Placed Object. In the image below, the item highlighted in green is NOT part of precombines but all the other references are, so if the mod does anything at all to those references with the brackets, it has broken precombines: 

Overlapping Items: If you repair a structure and have the old structure still visible, it is because you have a mod that is "clobbering" the cell header. Example of this in the spoiler below:

Spoiler:  

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Any mods that place new items (adding new items does not break precombines) in the cells affected by the Rebuild Previsibine patch need to be loaded BEFORE PRP (if using) and BEFORE the Rebuild Previsibine patch. The cell headers of the previs patches have to win any conflicts.

Open your entire load order in FO4Edit. If ANY other mods are clobbering the cell headers of the Previs patches (or the main mod if Previs is included or you aren't using the Previs/PRP patch), your load order is incorrect:

Previs is another way to improve performance by not rendering items that are behind something that is currently blocking your view. For example, if you stand in front of a wall nothing behind that wall is rendered. The less that needs to be rendered, the better the performance.

Items Blinking In and Out of Existence: Previs is generated for a 3x3 cell cluster, so a total of 9 cells (The map is divided into a grid of squares. These squares are called "cells") are included with the previs file (these are stored under Data/Vis). If you have more than one mod that regenerates previs for the same 3x3 cell cluster, they will conflict and you will get items that blink in and out of existence depending on the angle that you are looking at them. These type of conflicts usually require a patch for both mods to work together. This issue can also occur if a mesh crosses a cell border into another 3x3 cell cluster in which the mod didn't regenerate previs. To keep conflicts to a minimum, when I find a mesh crossing a 3x3 cluster border, instead of generating for another cluster which the Rebuild mod doesn't otherwise touch, I will remove that mesh from precombines so it won't affect previs.

All Rebuild mods break precombines, so I regenerate them along with previs in the previsibines patch. I transfer all fixes from PPF.esm (this does not mean you have to use it) when I regenerate them so that the previsibines patch can be used with or without any version of Previsibines Repair Pack (PRP) Stable Branch and those fixes won't be lost. These patches are included with the main mod download and should be placed very low in your load order.

I use PJM's Precombine - Previs Patching Scripts to create the patches (for the most part). I tend to create my own seed plugins though, instead of using the scripts to do it. This ensures that ONLY the required cells have previsibines regenerated and to make sure that every cell has precombines regenerated (this is how I'm able to make them work with or without PRP and are not PRP version dependent). Read the articles if you want more detailed/advanced info on previsibines and how you might possibly be able to patch your load order if you have conflicting mods.