If the landlord is asking for money in addition for "possession" (which is asking for you to be evicted), then you have to file an Answer or the landlord can get a default judgment for whatever amount of money the landlord claims.
If you are not being sued for money, then you may want to file an Answer to make your eviction defense easier. You should file an Answer before your eviction hearing.
What is an Answer?
An Answer does exactly what it says it does - it allows you to answer the landlord's claims in the Complaint. The landlord must prove 3 things to evict you:
The landlord is the proper party to evict you;
There is a good reason to evict you, such as nonpayment of rent or because the lease ended.
The landlord gave you the Notice to Vacate require to evict you.
An Answer allows you to dispute any of those things and explain other reasons why you shouldn't be evicted.
Complete the Caption
The top part of the Front Page of the Form Answer is called the "caption" and has the general information about the case. You should copy the Court name, the case number, the judge's name and the name of the Plaintiff from the complaint. You should also add your address to comply with court rules.
Admit or Deny each paragraph in complaint
The landlord's complaint should use numbered paragraphs, and if it doesn't, you can number the paragraphs yourself. If a paragraph in the complaint is true, you can "Admit" the paragraph by scratching off "DENY". If a paragraph isn't true, or you don't know if it is true, you can "Deny" the paragraph by scratching off "ADMIT". You can explain why you are don't think a claim is true or tell the Court to see evidence that you attached.
Add Signature Page & Affirmative Defenses
You must also complete the Signature Page form, because an Answer will not be accepted if it is not signed. You may also add Affirmative Defenses, which are reasons you shouldn't be evicted. You can add multiple Affirmative Defenses, as long as they are true in your situation.
Affirmative Defenses Available
Did the landlord accept future rent after giving you the Notice to Vacate?