Chidori can be very well used without activating Sharingan. Sharingan is only needed to nullify the Tunnel Vision Effect and to save yourself from enemies counter-attack.
But it seems Sasuke has a knack for both. Every time he resolves to use Chidori he lights up his Sharingan. Against a formidable opponent, it is fairly understandable to use both to avoid any chances but why such extra precaution against a simple rock? It's not like Sharingan is for free, we're all aware of the considerable chakra cost for the red eyes then why does he need to do it?
I've noticed it now twice, in Boruto
- Episode 61
- Episode 157
Why did Sasuke need to activate Sharingan to blow up the stationary boulder using Chidori?