land impact.

Land Impact. Explanation

prims start with their LI = prim count.
but,

once prims fit certain criteria,
using textures other than just diffuse ( materials )
using alpha masking
linked with mesh objects
they will use the 'new' LI weighted calculations.

in Build Menu > More Info button > Weights of Selected >

Download : | varies on parameters for prims |
Physics : | varies on scale & parameters |
Server : | varies on things that affect the server |
Display : | used for avatar complexity, not LI |
physics weight is often the greatest value - setting prims to the Convex Hull Physics Shape the value can be lowered.

there are potential caveats when using convex hull

▸object collision
▸avatar collision
▸you cannot sit on prims inside a physics shape without a sit target script
( even if the interfering object is set to phantom. )

you can visually inspect your prims physics shapes for these problems,

Preferences > Advanced > 🗹 Show Developer Menu

Top Menu Bar > Developer > Render Metadata > Physics Shapes
( you also can see the physics shape of individual prims. click the eyeball next to the physics shape type in the build menu. )

you can change individual linked prims physics shapes with 🗹 Edit Linked 

1. twisted torus with no materials, only diffuse. ( 1 LI, using the prim count as LI )
2. twisted torus with materials and physics shape still set to Prim. ( 128 LI )
3. twisted torus with materials and physics shape set to Convex Hull. ( 1 LI )