soffit vent channel/baffle installation

been looking to add some insulation and install soffit vent channel in the attic.
does the channel has to be installed in ** all ** the void between the rafters or just a few around where the vents are?
thanks richard
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The baffles are so the insulation won't cover the intake (vent). They are installed for blown in insulation. The bay created by the rafters will direct the intake towards the peak.
Some will argue you absolutely need baffles, but think about it b/4 putting them in. As long as you don't block the intake (vent), you will get the same result without them.
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