The overseers were there to ensure that the slaves did their allotted work. Did Pharaoh need the work? To some extent, yes. Without huge gangs of labourers his building projects would have been impossible.
But the phrase “to afflict them” indicates something more than imposing a daily tally of work. It implies a policy of trying to break the spirit of the Hebrews, to afflict them and bring an end to their will to live. This would be measured by their no longer wanting to bring children into the world: why have children when there was to be no future?
Ibn Ezra accepts this view, which is borne out by the next verse, “The more they afflicted them, the more they multiplied”. Pharaoh’s policy of reducing the Israelite population did not work: the harsher the treatment, the more they determined to rise above it.
But why should Pharaoh shoot himself in the foot, so to speak, by keeping down the numbers of the Hebrews and thus denying himself a labour force?
The answer is suggested by verse 10, which shows that the king was apprehensive that the slaves would conspire with outside enemies of the regime and together make a mighty effort to cause a coup d’etat and oust Pharaoh and his government.
Tyrants always live in fear that they will be toppled, and they usually are. In many cases they themselves come to power as the result of a coup, and they never feel safe.
In regard to Pharaoh the verb Vayyakom, “and there arose a new king over Egypt” (Ex. 1:8) seems to prove this.