Limitless
The 24 hours given to me at the system space every time I clear a stage or leave a domain were undoubtedly a very precious gift that had many beneficiary uses, including isolation requiring procedures, buying stuff at the system shop, and even pure luxury, but the main use that shone the most was training!
All kinds of training usually require special environments, some would even argue that they would do well at something if it was done at the right place with the correct factors, and while that is not completely true, this whole 'right place, right factors' theory does indeed have some points to prove.