The active ability of the ring is
Toggle controls only whether armor bonus applies to non-Hero units.
I tried turning it off and on, but it did not affect its effect on my hero.
Is there a downside to leaving it always on? When should I switch it off?
Best Answer
There are three main reasons.
When you are giving an armor bonus to your creeps, you will end up pushing your lane towards the enemy, which is something you do not want to do as you're granting them improved safety and risking a gank to yourself.
Sometimes, you may want to toggle it on and off randomly when in lane to mess with the enemy hero timing in their attempts to last hit your creeps.
As AdamP pointed out in the comments, the aura may give you away if you are invisible or hiding nearby.