The cam designer determines a spec. In the case of MP I've always found the factory recommended lash was too lose. It's been a while since I ran MP but in the past mine liked about .006" tighter than what MP wanted. Some modern stuff likes a tighter lash due to the take up ramps and lobe designs.
That beign said the engine materials and actual engine build may mandate changes from that recommended spec. I usually set mine on the lose side to get things up to temp. With iron i'll reset them hot. With aluminum I run it to get it to temp, then reset one head hot, run it again to reheat eveything, and reset the other head. Once that's done you can mess with the lash on back to back pulls (or runs) to see what it likes. But also as IQ hinted at - if you have to go too far you probably missed a little on the cam choice.
