I check mine evey time I service it,and I think I've only adjusted it about half a dozen times.
If you don't adjust it when the gap gets too big,the movement will just get bigger and bigger I suppose,and the pushrods won't line up properly,and they'll wear more and more,and push to one side,and then it'll throw a rod on the motorway,all the oil will come out,and the 40 tone truck behind you will skid on the oil,crash into a coach load of children and burst into flames,taking out the other carrigeway in the proccess.And just because you didn't adjust the end float.How will you ever live with yourself*
*This MIGHT not happen