[idlewords]

Not having a model is better than using a model based on imaginary data, which is what you'll have until you launch your site. As other people here have pointed out, traffic for new sites is very bursty and depends in large part on who links to you when.

[lowkey]

I call bullshit. The purpose of making a forecast is not to predict the future, it is to identify errors in the logic of your assumptions. The experienced business guy is simply putting together a model based on obviously fictional data to help understand the financial dynamics of the business - probably to see if there even IS a real business.

It's nice rhetoric to proclaim that since user adoption figures cannot be predicted with accuracy, they should not be predicted at all. Even without accurate forecasts, it is trivial to calculate the required breakeven users and examine scenarios where that breakeven is achieved in a short,medium, or long ramp period. Other valuable metrics are also more easily discerned from a model than by pure guess.

It sounds like me that that business guy is simply doing his job - and it sounds like he knows his job better than many readers here.

[idlewords]

You don't need to badger your devs for anticipated traffic figures in order to calculate those kinds of scenarios. It's one thing to calculate various thresholds and set up hypotheses that you'll test later, once you've collected real data. It's another thing to make numbers up out of whole cloth so you can fool yourself into thinking you understand more than you do about your business.