Generally when estimating using an Agile points system on an experienced project team, the points have meaning relative based on past experience - that take into account:

• understanding of the business domain
• skill and experience of the team
• obvious traps in the technical environment (service integrations and environment issues)

So based on the past velocity of the team - you can forecast how long a project is likely to take.

Now imagine a completely new team thrown into a new business problem domain, new technical environment, with unknown skill levels. You can estimate with points, but you have no velocity track record.

Now you can augment this lack of historic velocity with a 'default velocity' - with the caveats that the three factors above are unknown, and so your tolerance for delivery date is much higher.

But is there an agile reason not to do this?

My question is: When estimating with a fresh team on a new project, is there a reason not to use default velocity for estimating?