precomp can be triggered in many ways but you would find the one which suits you. There is precomp with jpg compression, for games like pro evolution soccer, the game img's has alot of images therefore precomp works well than any other compressors if more pressure is applied like precomp+zip/7z/rar/arc.
then there is precomp without jpg compression(zlib compression) which searches thoroughly for repeated sector/sections of a file then then makes those repeated sections/sectors as one to save space. for games like Need For Speed The Run.
Code:
-mprecomp:t-jnf:zl31,34,39,44,55,64,67,68,73,74,75,84,85,94,97,99:d0+srep+exe2+delta+lzma:a1:mfbt4:d158m:fb273:mc1000:lc8