Super quick and simple thing that some might not know.
If you go into your Side Effects Software Install folder you can follow the path over Houdini Version>>houdini>>vex>>include and you will find a pot of pure gold.
These include files are a library of functions and constants that are useful for one specific topic like crowds or grooming. They can be included into each wrangle Whenever you need their content. This would also be the place to create your own helper files using these as a template.
Using them is fairly easy - just write #include <file> at the beginning of your Wrangle and use all the functions or constants it holds.
But there is more to be found. You can also find useful notes that you will not find in the docs. Like the defintion of those parameters from maketransform() found in math.h
Another good reason to take a closer look into those files are some very useful functions like being able to adjust the length of a primitive found in groom.h
void adjustPrimLength(const int geo, prim; const float currentlength, targetlength)
You can either just use them directly or/and take a closer look at the coding. It is a great source for VEX learning.