I too would like to see any links to the mentioned RA "recommendations"
Having heard the same "don't use the continuous task" directive, I spent some time looking for a written Rockwell reference. Based on a review of the links below, as well as numerous message-board posts, the closest I could find is in the 2007 version of the Logix5000 Controllers Design Considerations Reference Manual (Publication 1756-RM094C-EN-P - June 2007), under the "Configure a Period Task" heading:
"If your application has a lot of communication (such as message instructions or RSLinx communication), use a periodic task rather than a continuous task. This avoids the overhead associated with task switching, which can improve performance."
This statement has been removed from the 2019 version (Rockwell Automation Publication 1756-RM094J-EN-P - September 2019), nor does it appear in other, newer publications.
I will just say that my opinion on this is that not using the continuous task, as a matter of policy, leaves significant system-provided functionality unused. For reasons mentioned earlier (e.g., interprocess communication), I limit my use of periodic and event tasks to instances where their benefits are necessary and/or justified.
Refs:
Logix 5000 Controllers Tasks, Programs, and Routines
ControlLogix System
Logix 5000 Controllers Design Considerations
Using Event Tasks with Logix5000ô Controllers
Technotes (access Everyone unless noted):
RSLogix 5000: Differences Between Continuous, Periodic, and Event Tasks
Periodic Tasking with ControlLogix (Tech Connect)
RSLogix 5000 Tasks, Programs & Routines
Logix Platform : Task Priority Levels within Logix Processors
Configuring the System Overhead Time Slice
RSLogix 5000: How to avoid Task Overlaps (Tech Connect)
When a timed task is enabled my ControlLogix processors program scan time increases to an unacceptable level (Tech Connect)