35mm+ clearance isn't necessary for everyone, but it's ideal if your riding includes rough pavement, dirt roads, or light gravel. It gives you the freedom to run wider tires at lower pressures, which dramatically improves comfort and grip on imperfect surfaces. Think of it as insurance — you can always run 28mm tires on smooth days, but you can't fit 35mm rubber on a frame built for 28mm max.
This kind of clearance is most at home on all-road and bikepacking road bikes, where versatility matters more than pure race performance. The trade-off is a slight weight and aerodynamic penalty compared to tighter-clearance race frames.
If you stick to smooth tarmac and care about every watt, 28–32mm is plenty. But if your routes venture beyond perfect pavement — or might someday — 35mm+ clearance keeps your options wide open.