if you don't respond and contest the foreclosure, it will enable the Plaintiff to move the case faster, and they will not be obligated to do much of anything to prove their case. If you don't care whether that happens or not, you don't need to respond.
Just be aware that they are these days including a claim for deficiency judgment in most foreclosure actions, and so if they realize less than the total amount owed, they can come after you for the difference.
I agree with Ms. Golant's answer. Also, bear in mind that if you are defaulted and don't monitor the case, you have no way to know how much the Plaintiff will claim for damages, fees, costs, etc.
Although it has hazards of its own, if you are the defendant, you are allowed to file a response in your own name.
You can also try to negotiate with the lender, but be aware many are not very interested in negotiating.
You may wish to contact your local bar association -- many are offering pro bono consultations on foreclosure defense.