Slow response when not in server role

[trier]

I have a user that accesses a cube via excel 2007. If they connect to the cube and start loading dimension data everything works ok until they get to about 6 dimensions at which point the response back from analysis services cube becomes very slow (minutes). However if I add that user to the Analysis services server role then the response time back is greatly improved (seconds). The cube role the user is in has access to all dimensions. Does the user have to be in the server role or is there something else that needs to be set up.

Thanks