Answer:
To allow all the elements or compounds to separate complete.
Step-by-step explanation:
In chromatography, the compounds need some space and time to separate, one from each other, if you just use the half of the paper strip maybe you will not notice the different spots of compounds. Remember all the substances have different affinity for the solvents, that means, some react very quickly but others need more time as the colors that conform the black color in an ink.