Currently preprocessing manager attempts to refresh configuration (preprocessing steps for all items, dependent items, internal items) whenever an item preprocessing request is received. The data is synced if any item were synced from database since last preprocessing configuration refresh.
With improvements in configuration cache sync and possible decrease of sync times, the preprocessing configuration refresh will be performed more often and have more noticeable performance impact. Also because of incremental configuration sync server will cache preprocessing data also for items monitored by proxies (to track revisions), increasing preprocessing configuration refresh.
Investigate possibility of revision based incremental preprocessing configuration refresh. This will be based on host, hostmacro, global macro and regular expression revisions like it's being done with proxy configuration sync.