Knowing the % of the company your grant represents allows you to deduce the current valuation of the company, which is considered by many companies to be secret.
It also lets you put a value on the equity portion of an offer. W/o info to price that, you might as well value it at zero.
That said, I don't think I've ever interviewed with a startup that gave me an offer with equity that wouldn't share # shares outstanding, amounts invested, and liquidity preferences. If a company won't share that at the offer stage, I'd have concerns.
Also you have no influence over future rounds, so a good equity deal now could easily be worthless in the future (or even worse, negative returns due to taxation on paper gains that subsequently disappear).
Concentrate on your other benefits, whether you think the founders and investors have integrity, and whether you think the market opportunity might be a winner.
No big disagreements here. The numbers are mostly useful in determining if the equity offer is "fair" or at least matches how the company has described it. That goes to their integrity.
Which is a bit silly as the price per share of the last preferred equity financing round and the authorized number of shares are filed in the corporate charter which anyone can access. That gives you at least a lower bound on the valuation.
That's a question I've always used personally, and I've refused offers from companies that wouldn't answer it.