Why is mobility important? Long story short mobility keeps you young. It's one important aspect that keeps you functioning like a normal human. There are plenty of conversations where we've realized our mobility is slowly fading and they all start with "my back hurt".
To reduce feeling 1000 years old and to properly continue on your muscle building journey continue your mobility exercises and moving in different directions in your workout routine. Specifically for your core, cable rotations are an awesome and easy exercise to hit your abs at a different angle (aka your abs will be more shredded), keep you strong, and make sure you don't age 50 years overnight. Just imagine life restriction free (in terms of mobility) as you pack on some serious size while you're doing this exercise.
3 sets and 8-12 reps