3 : Why b- or a-tier ? I guess to attract better players. That's what did it for us, anyway. We held the 10th edition of our tournament as a B tier for the first time, and it attracted some of the best players in europe, for example the euro tour winner and the current open and masters european champions.
Around here, higher tiers generally attract more players. Not just more top players---more local pros and advanced and recreational and the rest.