When a client roams, it's supposed to send the AP a disassociation packet with information about the roam. However, if a client simply shuts down or otherwise roams and is unable to deliver this packet, the AP needs to know to clear it out somehow. As such, when a packet is sent to a client X number of times, and the client never responds, the AP assumes that the client is no longer associated and drops it.
Increasing the amount of retries is probably not a terrible idea. The "problem" is that it will take an AP much longer to decide that a client is no longer there. The only disadvantage I can think of is that the client will remain in the association table longer, and this is only a problem if you have a client limitation on the AP. Your AP will also repeat a packet 128 times to a client that isn't there, thus consuming bandwidth. But 128 packets isn't exactly a ton.
Really, it's just a matter of keeping things clean and tidy. You want your APs to know when a client is no longer there, but you don't want it to prematurely drop your clients. I would try to reduce it as much as possible while still maintaining client associations.
Jeff
