return-by-reference for Object field access

[schmoozerd]

Can somebody explain why we use return-by-reference to access object-fields?

        const int32& GetInt32Value(uint16 index) const
        {
            MANGOS_ASSERT(index < m_valuesCount || PrintIndexError(index , false));
            return m_int32Values[ index ];
        }

        const uint32& GetUInt32Value(uint16 index) const
        {
            MANGOS_ASSERT(index < m_valuesCount || PrintIndexError(index , false));
            return m_uint32Values[ index ];
        }

        const uint64& GetUInt64Value(uint16 index) const
        {
            MANGOS_ASSERT(index + 1 < m_valuesCount || PrintIndexError(index , false));
            return *((uint64*) & (m_uint32Values[ index ]));
        }

        const float& GetFloatValue(uint16 index) const
        {
            MANGOS_ASSERT(index < m_valuesCount || PrintIndexError(index , false));
            return m_floatValues[ index ];
        }

        uint8 GetByteValue(uint16 index, uint8 offset) const
        {
            MANGOS_ASSERT(index < m_valuesCount || PrintIndexError(index , false));
            MANGOS_ASSERT(offset < 4);
            return *(((uint8*)&m_uint32Values[ index ]) + offset);
        }

        uint16 GetUInt16Value(uint16 index, uint8 offset) const
        {
            MANGOS_ASSERT(index < m_valuesCount || PrintIndexError(index , false));
            MANGOS_ASSERT(offset < 2);
            return *(((uint16*)&m_uint32Values[ index ]) + offset);
        }

        ObjectGuid const& GetGuidValue(uint16 index) const { return *reinterpret_cast<ObjectGuid const*>(&GetUInt64Value(index)); }

instead of normal return by value?

(Historical note: we do this since long forgotten times)