I clean my juicer after each and every juice I make... the pulp hardens on the screen mesh and the other attachments making it real work to clean later. And a dirty juicer can be a health hazard.
It is highly recommended that you drink the juices as soon as they have been made. Freezing them for later is probably the least hazardous to the juices, then say, popping them in the fridge for later consumption. But, even freezing damages some of the nutrients and enzymes. But it's better than not drinking juices at all and it's better than storing it in the fridge. But the best is to make the juice and drink it down then and there.