Hi, Patricia. Selling and buying at the same time, especially if the proceeds from the sale are needed to purchase the next home, require skillful coordination between the two transactions. Having the same Realtor, title and escrow can help streamline the process. Many agents will give a break on commissions for multiple transactions.
The disadvantage, of course, is that if you're unhappy with the service provided by your agent, you would be doubly unhappy!
Hope this helps!