The point is that if you're already fully invested you don't have money to buy those additional shares. And if you didn't want the leverage before, commiting to take on leverage later may or may not be a wise thing to do.

It may make sense if you had dry powder waiting for a correction. But at that point you are forced to buy (and as you say it may be at a higher price that the prevailing one in the market). You get premiums but you lose flexibility.