Thinking about self-representation in civil actions and the cost of professional representation by a lawyer, a quick cost-benefit analysis suggests that self-representation is always recommended when the cost of professional legal representation is greater than the cost of doing nothing, but the cost of doing nothing is greater than the cost of doing something on your own, without a lawyer, even if it is wrong.
Is it ever a good idea for a defendant to allow a default judgment to be entered? I cannot think of one. There is a risk involved with asserting frivolous defenses for improper purposes, but there is usually always some legitimate defense to be offered at the cost of a few pieces of paper and a postage stamp. Even if the only defense available is to take issue with the rate of post-judgment interest imposed, it is better than doing nothing. It is better than a default judgment.
Appearing and defending an action keeps open the door to negotiation and settlement. It provides a certain extra amount of breathing room to review, research, verify and maybe even talk to a lawyer about the case. By appearing and defending, a defendant continues to receive pleadings and notices in the action, which are not required for a party in default.
This is not legal advice. This is practical advice. Never allow a default judgment.