Several folks have inquired why AutoCAD MEP 2013 seems to regenerate slowly compared to 2012.
This is an intentional addition to the 2013 products called ‘progressive update’…. What it does is allows you to make modifications during the regeneration of hidden lines, so you don’t have to wait in the case that generating hidden lines is very time consuming… for example, when you have many drawings xreferenced together.
You can turn it off using the command SETENABLEPROGRESSIVEUPDATE… then the functionality will return to as it was in 2012. This is a profile wide change that will be retained across all drawings, and re-starts of the application.
Here is a video demonstration: