The cooking-attic problem
An unventilated attic hits 150°F in summer — baking shingles from below and voiding some warranties — and condenses moisture in winter. Shingle life is as much attic climate as shingle quality; the replacement is the one time fixing it costs almost nothing.
The balance: intake and exhaust
Ventilation needs intake (soffit vents) AND exhaust (ridge vents) in rough balance — exhaust without intake just pulls conditioned air from the living space. The 1/300 rule (1 sq ft net free vent per 300 sq ft of attic, split intake/exhaust) sizes it; a reroof is when ridge vent gets cut in and soffit baffles get checked.
What to ask for
Continuous ridge vent with proper soffit intake, baffles at every rafter bay (insulation blocks soffit airflow), and sealed attic bypasses (bath fans, can lights) that leak heat into the attic. The line items add a few hundred dollars to a replacement and add years to the shingles — the best ratio on the whole quote.