I am not a lender, but verifying income seems vital to the process.

LOL you do not get the award for silliest questions but you're certainly in the running! 

ANSWER: ONLY if we wish to avoid another mortgage cluster like the last bust! But otherwise, go ahead and give that ham sandwich a loan! LOLZ

I wasn't sure if this was a serious question since it's such an obvious answer.
But, I'll let Jason E. Gordon educate you.

Well, under the new ATR (Ability to Repay) rules, on must prove they can repay.  No more "Yeah, I'll pay you back" loans exist.

Heavy vetting with no exceptions is what I found & that's the process buyers must meet & qualify according to lender specifications not theirs or mine

Debt to income ratios is used to determine credit approval when applying for a mortgage. At some point, lenders may even ask to see your IRS tax records for verification. This is certainly true for the self-employed. 

Ever since the 2007 Housing Crisis, the Government has put immense pressure on lenders to demonstrate "Ability To Repay" (ATR) when approving a Borrower. In my opinion, we have over-corrected on this topic...hoping for some leniency to someday reappear for Self-Employed borrowers.

Income Verification is required to get a traditional loan.  This would prevent loan approval if income is not verified.

An experienced mortgage broker with a plethora of funding sources may be able to direct you to a program where there are alternatives but the price of entry is high. In normal circumstances income verification is critical since it determines what you can pay.

Yes. 

It depends on the amount of income, the loan and the lender's requirements. 

Depends on the loan and transaction type.  For most residential loans it's a vital piece of the puzzle.

I think yes.  But I also have a 22 year old mortgage that was no doc.  

It should be, but I hear that some lenders are doing Stated Income!!!

My answer is that it is required.  

I let the lender take care of verifying income for the buyer. It is a normal part of the approval process.

If I were lending money, I would want to know how it was going to be paid back.

It depends. Bring back "Stated Income" loans!