dash bar question

torkflight said

for an 8.5 cert bar there is no spec on height, its pretty obvious, it will be lower than the windshield and high enough that your knees wont bang on it, and it is not required on an 8.5 cert cage if the firewall has not been modified more than 1 square foot.

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Why would one not put in a structural significant bar under the dash if they are going to add a cage in the first place??? If one wants to upgrade later to go faster down the rosd. Perhaps it being there already will savr them the hassle and cost to do it now.