Hi Ganesh,
There are workarounds or a workflow can be configured using approvals to ensure that an auction with a single supplier does not get published accidentally. Even if it happens there is always an option to edit the event to update missing suppliers.
Having said that, there could be a need for record keeping purposes say as a company policy to get the bid recorded in an auction where no real auction case feasible/exists. Say you have a offline bid from the vendor and so to get it into the system you create the auction with single vendor and surrogate bid.
This is a completely hypothetical and personal view and off-course not a reccomendation.
Cheers!!
Vilas