Castor Angle

This has probably been dealt with on thread somewhere already. If it has just point me in the right direction. Whats the general concensus on castor angle for carts?. A clever sort of chap advised me not to bother with it but I ve built my front steering as a weld/bolt on unit and am now ready to weld/bolt it on and if I want to I can tilt it a wee bit to gve some castor angle. If I was really clever I could hinge it so it could be altered to suit the course. I suppose it all depends on how twisty turny or straight a given course is. Waddaya all think?