Confusion about DTLs/DTAs

Can someone please clarify when a DTL/DTA is created? I've read way too many contradictory posts now...

According to Wall Street Prep: https://www.wallstreetprep.com/knowledge/financia… As the example above illustrates, the DTL is created to reflect that due to different book vs. tax depreciation rates, there is a temporary timing difference leading to a lower payment to the IRS than reported for book purposes.

Also from Investopedia: https://www.investopedia.com/ask/answers/052915/w… Consider a company with a 30% tax rate that depreciates an asset worth $10,000 placed in service in 2015 over 10 years. In the second year of the asset's service, the company records $1,000 of straight-line depreciation in its financial books and $1,800 MACRS depreciation in its tax books. The difference of $800 represents a temporary difference, which the company expects to eliminate by year 10 and pay higher taxes after that. The company records $240 ($800 × 30%) as a deferred tax liability on its financial statements.

So to my understanding when book taxes > cash taxes then the DTL goes up.

If that's the case, how come in a M&A deal structured as a stock purchase, when we write up assets on book accounting without an equivalent step-up on tax basis, we have an initial DTL created? If we write up assets without tax basis step-up then the D&A expense is higher for book vs. cash accounting, and therefore book taxes cash taxes. This contradicts the above example. Or is this the wrong way to think about the DTL creation?

Subsequently, in future years, when we are able to amortize the written-up intangibles/PP&E in book accounting but not tax accounting, we again have a temporary difference in tax obligations. As a result, book taxes cash taxes again since you'd add back the amortization (it's not tax-deductible under tax accounting) to get taxable income. When this happens, we log a decrease to cash flow as well as a reduction to the DTL. Once again, this example seems to say that book cash taxes implies DTL down and book > cash taxes implies DTL up. How come when we adjust balance sheet proforma for M&A/LBO transaction we have DTL going up with book cash taxes?

EDIT: Seems like this link Breaking into Wall Street has a post that sort of explains this confusion.

Instead of thinking about the company’s historical situation or its taxable income, think about its FUTURE TAXES. If future cash taxes exceed future book taxes, a DTL will be created. “Wait a minute – why does a DTL get created immediately? Isn’t it caused by the book and cash taxes being different many times historically?” Nope, not necessarily – that CAN be a cause, but DTLs/DTAs can also be created by events that change the company’s FUTURE tax situation. So you need to think about how taxes will change in the future, not how they’ve changed in the past, to determine this. “Wait a minute, the taxable income for book purposes is LOWER than it is for tax purposes – doesn’t that create a Deferred Tax ASSET (DTA) instead?” Nope. The relevant question is not how the taxable income differs, but how the FUTURE TAXES will differ. If the company will pay more in cash taxes than book taxes in the FUTURE, as a result of these write-ups, or any other changes, then a DTL gets created.

Perhaps my understanding of stock purchase structured M&A/LBO transactions is faulty. Can someone clarify it more clearly? To my understanding there are 3 steps. 1) Under stock purchase, book value of assets written up to fair market value; meanwhile, tax basis is not stepped up. (What effect, if any, does this have on DTLs?) 2) Goodwill is not amortized and is not tax deductible. (What effect, if any, does this have on DTLs?) 3) The written-up book value of assets experiences D&A subsequently and is tax-deductible for book purposes but is not tax-deductible for tax reporting? (Apparently this is the part that decreases/reduces the DTL amount over useful life?)

In contrast, for asset purchase we have step-up in tax basis + tax deductible D&A and goodwill is amortized over 15 years???