At what stage during modding should one be considering (or actually needing) a TS reflash in order to have a safe a/f ratio?

example: if all you plan on doing is intake, plenum, header, hf cats, exhaust, pulley... is that gonna mess up the a/f ratio too much? how about if you add cams to the mix?

 

i think it's when you have enough mods that your a/f is too lean to be safe driving hard for long periods of time...

 

yeah i realise that,... i just wanna know /when/ that point is... ie, what mods or mod-combinations are significant enogh to start needing a reflash to prevent unsafe a/f mix....