Handling performance: most important chassis bracing/reinforcement – per application?

This might be a good resource to collaborate on for this particular forum...but I'll need your help because I don't have enough first hand experience to say for sure what is needed. My guesses could end up wasting peoples' money.

This is what I'm thinking: For each application, which chassis reinforcements do you see as the most valuable? Which ones are absolutely critical? Perhaps list the type of bracing and what it accomplishes?

These are some suggested categories, feel free to...

Handling performance: most important chassis bracing/reinforcement - per application?