Business runs on deadlines and milestones for a simple reason - Time is Money
Those paying for the development of a product or service have an expectation that they will get the value from their investment on some date in the future. The longer they wait for the Value to be returned the less their Return on Investment.
Time is Money - Ben Franklin's advice to a young tradesman
In the Agile world the phrase deliver early and deliver often is good advice. In the traditional project management world, that phrase is deliver as planned.
But how early and how often? Agile developers like to toss that phrase around as an alternative to having a plan for the delivered value we'll replace planning and estimating with early and often delivery. But that doesn't answer the simple question. What the cash flow demands from the funders in exchange for the Value delivery look like in the Balance sheet.
If the business has a needed Capabilities, that Capability has a bookable value from a financial management point of view. That Capability, in turn, generated revenue, reduces cost, increase effectiveness or does something to improve business operations. The time value of money is the basis of decision-making in any non-trivial business spend.
So a deadline or a milestone of when the business cam start accruing the benefits of the investment (the cost) of the capabilities is a core business management function. In order to make those decisions about spend, revenue, value, benefits - Never Forget
There is NO means of making credible decisions in the presence of uncertainty without first estimating the outcome of that decision. This is a foundational principle of the microeconomics of probabilistic decision making. To suggest you can make such a decision without estimate requires you intentionally ignore this principle.
So remember, those paying for your work have a fiduciary obligation to spend their money wisely. These means they need to know when they'll get their money back and how much they'll get back.
So do we pick a Capabilities Release or a Cadence Release?
Capabilities release provides the answer to Early and Often. When we have something of use to the business, let's release it. This approach, by the way, doesn't seem to consider is the business capable of putting that capability to use, but that's a separate issue.
Cadence release puts value out on a periodic basis. All the users know the dates and what they plan on getting. Those capabilities don't always show up in the Cadence, but that's a separate issue as well.
In both cases, estimating is needed. For the Cadence Release, we need an estimate (with accuracy and precision) of the probability of showing up with needed Features on the needed Date. For the Capabilities Release, we need an estimate (with needed accuracy and precision) of the probability that requested Features will be in the release.
Business runs on confidence that they will get their money back as planned at some needed time in the future. This means estimates are part of business management. Not making estimates in the presence of uncertanty, you're not managing the business.