* A. You cannot use navigation attributes for this characteristic: This is a disadvantage of setting the High Cardinality flag for a characteristic. A characteristic with high cardinality cannot be used as a navigation attribute for another characteristic, and therefore it cannot have navigation attributes itself12.
* C. SID numbers are created at runtime which might negatively affect the reporting performance: This is a disadvantage of setting the High Cardinality flag for a characteristic. A characteristic with high cardinality has no persistent SID values and no SID table, which means that the SID numbers are generated on the fly during query execution. This can have a negative impact on the reporting performance, especially if the characteristic is used in filters or aggregations13.
Reference:
* 1 https://help.sap.com/docs/SAP_BW4HANA/107a6e8a38b74ede94c833ca3b7b6f51/f851415842154e59a5f038e458b97a0b.html
* 2 https://help.sap.com/docs/SAP_BW4HANA/107a6e8a38b74ede94c833ca3b7b6f51/88a51330c046426091f3730d0c42c0de.html
* 3 https://blogs.sap.com/2019/01/14/high-cardinality-characteristics-in-bw4hana/