Also many blades are not heat treated so they dull faster but said by IL .030 is considered sharp. Even when put on a new sharpen blades they dull somewhat the first cutting. It is the major rock (impact) damage that is more concerning. I do install heat treated blades here and they do last up the 2X as longer as OEM blades. So far I haven't quote heat treated blade for the MTD 46" decks; although, the MTD blade style I from Stens looks to be very good blades and they are .164 thick.
I would only sharpen when the quality of the cut becomes poor. Different grasses wear the blades differently so there is no fix time frame as to when to sharpen.