The reason for PICUS is to allow an FO with less than 250 hours PIC to get an ATPL: A CPL requires 100 hours as PIC, whereas an ATPL requires 250 hours (ignoring the MPL route for the purposes of this explanation) which can be made up of a combination of PIC and PICUS.
The most PICUS you're likely to need is therefore 150 hours, logging any more than that is pointless and could even count against you if for example at interview an airline thought you were trying to pad your logbook with Jet "command" time, despite never having passed a command course or flown LHS.