Tax return filing requirements

Hello!  I know that you are required to file a tax return when your total income exceeds a certain minimum amount.  However, I have heard that in certain special cases, you are required to file even if your total income is below the minimum income threshold amount (particularly if you have self-employment income).  Are there any other cases when you'd be required to file regardless of total income amount? 

I ask because I was wondering if making an early withdrawal from a Traditional IRA would cause you to be required to file even if you are still below the minimum income threshold with the rest of your income included.  I know in some cases it is worth it to file even if you're not required.  I did have Federal taxes withheld on the withdrawal.  Since you're usually penalized for withdrawing early, I was wondering if the benefit of getting the withholdings refunded would outweigh the penalty.  I'd appreciate any feedback on this matter.  Thank you!