Multiple SMTP address impact on Exch55?

I’m running Exchange Server 5.5 SP4 with under 100 mailboxes on a Dual 600Mhz PIII with 512MB.
If I created 2 or 3 smtp addresses for each user, would I see any performance issues? What downside is there for this procedure?

The reason for this would be to convert from a first name – last initial naming convention to the opposite.

Thanks