Every bank is different, but an underwriter and a loan officer serve two very different functions. Of course it benefits the company if they close a GOOD loan. The loan officer's job is to attract qualified applicants and assist them in getting the loan, but the underwriter's job is to evaluate your loan application and make sure it's a good loan- that you meet qualification requirements and that the bank is not taking too much of a risk with lending you a large sum of money.
Loan officer's are generally paid by commission on loans which actually close- although some banks pay a small salary as well. Underwriter's are generally paid a salary and are paid whether your loan is approved or declined. Although they may receive a bonus for hitting certain goals with regards to GOOD loan approvals or in having no deficiencies in their file if the loan happens to be audited later on.
In your other post you had mentioned time turnarounds I think. Every lender has different turn around times which could range from a day or two up to several weeks. And this varies depending on traffic levels as well. It all depends on how many loans are in process at a given time, what the quality of the loan applications are, and what resources a given bank or lender is going to devote to the underwriting process.
A lender that rhymes with Sicken Loans may have dozens of folks involved in the processing and underwriting of your file and may get it done in a very speedy fashion. But the rates and fees you pay may be impacted by so many cooks in the kitchen. Another bank that rhymes with Smells Fargo may have a 30 day backlog of files waiting to be looked at and their resources are tied up elsewhere. But the rates are so good most people will wait. Most good lenders will strive to get you an answer in a reasonable time - 2 to 3 days- but realize that depending on the complexity of your individual loan application there may or may not be additional conditions added.
It all goes back to who you select to handle your loan from the get go. Hope this helps!