The Sharingan would be a relatively useful tool if he were to wield it just as effectively as an Uchiha (minimal strain), but the Cursed Seal would magnify the chakra consumption of Shikamaru's techniques which have proven to be an encumbrance for Shikamaru. The Sharingan would prove to be effective for Shikamaru who pivots on his analytical ability, something he is admired for and subdues his opponent through clever and elaborate diversions rather than chakra intensive techniques. The only moment where it'd be effective is in short bursts against an opponent with potent chakra (Kinkaku) in a team-based scenario, but other than that, it wouldn't be as effective as someone else had argued before.
I don't think he'd be extraordinarily powerful if at all honestly. The best it would do is magnify the binding power of his shadow and possibly increase its speed as well which is good, but Shikamaru's diversions are his forte, not sheer speed/power.
