What is an accounting estimate IAS 8

An accounting estimate involves judgement by management based on the latest available information at the time.

Estimates include:

1. The fair value of financial assets and liabilities
2. Useful life of property, plant & equipment / depreciable assets
3. Expected credit losses
4. Inventory obsolescence
5. Debt provisions
6. Warranty obligations

A change of accounting estimate is accounted for on a prospective basis (going forward, not looking backward).

Who cares?

Auditors might.

You, because you will likely need to guess stuff, as estimating can be in essence, good old "guesswork".