Poor troops? I'd guess that it depends a lot on situation, in the open, facing disciplined mobile units, mass levy's or militia will be cut to ribbons.
With a strong commander who can bully them into a semblance of order, able to attack from a flank and break their enemies formation, or fighting in woods/swamp where heavy armour is a hindrance and formations impossible, the irregular type troops would be quite effective. Another use is simply in mob war - a single unit of elite knights will be slaughtered by a half-dozen militia units if they surround it even though it is more costly than the accumulated levies.
Remember that we aren't talking about people pulled away from desk jobs, we are talking about farm labourers mostly - people who work in manual labour day in day out and are used to wielding polearms, axes, clubs, etc in their workings lives - that said they are a long way from military, particularly if their shaky formations are breached (they have no internal cohesion and are easily tempted into strategic errors having no military experience).
The real downside of levies is that these are not 'surplus' population, but the blood and bones of the economy - slaughter or capture them and your enemy is left economically crippled not just militarily. Ransom is the order of the day...