From personal experience regarding Command Practice,
My company preferred you to log CP if you were the Flying Pilot. The company SOP's essentially gave all Capt's permission to supervise Command Practice provided both crew were out of the 3 month probationary period after being checked to line in their respective role. It went further to go on to say it should be discussed at the start of the duty and it should be meaningful experience.
Command Practice was recorded on the company trip records and that met the CAA requirements as, it would be possible, but impracticable to get the skippers to sign off each entry.
It was said to me that Command practice time was considered important because it showed (particularly in interviews) that you didn't just sit there as a "co-pilot" doing as you were told, but making the necessary decisions to complete the flight safely (using appropriate CRM of course). I still log CP as an F/O even with my ATPL.
Hope this helps
S2K