Prior to Environment Manager 8.3 a Personalization Server was configured within the Environment Manager configuration.aemp file. When the agent started it would read the configuration.aemp file, connect to the first available server listed. The connection would then be subject to the sites list within the Personalization Server console to determine which Personalization server the end user would access. The problem with this implementation is each machine would perform this evaluation, each user who logs on would perform this evaluation and then each time the configpoll is triggered (default 600 seconds.)
As you can imagine the above means there are quite a number of hits on the database for each user. Take this and extrapolate it out to your total user base and it gets you thinking.
What AppSense did to address the issue is make a few simple changes. The first was allowing Administrators to configure a Personalization Server using ADM or ADMX actions. These can be configured using either a User or a Computer policy and can be enforced using Group Policy or AppSense Environment Manager Policy. The second was change the configpoll value to 86400 seconds (24 hours.)
The combination of the above make a massive difference on Personalization Server scalability and I personally see no reason not to implement both of the above changes.
The following flow chart shows the order in which the ADM / ADMX actions apply when compared against the traditional configuration.aemp method.
The only tip I do have is if you opt to specify the Personalization Server using User Group actions i'd suggest implementing the ADM / ADMX actions using traditional Microsoft group policy.