Move water away from the roof—and the property.

Not on their own. A larger gutter holds more water, but gutters rarely fail because the trough was too small — they fail because the water arriving at one point exceeds what the outlet there can take away. A long roof draining into a single downspout will overflow at six inches just as it did at five. The useful questions are how many outlets there are, where they are, and where the water goes once it leaves them.

Sometimes, and the deciding factor is the edge rather than the calendar. If the drip edge, fascia or roof-edge detail is being disturbed by the roof work, doing the gutters at the same time avoids taking the same components off twice. If the gutters are sound and the edge is not being altered, replacing them alongside the roof is spending money on their age rather than their condition.

Usually capacity or fall rather than blockage. North Texas rain arrives in short, hard bursts, and a run with too few outlets, an outlet in an unhelpful position, or no consistent fall toward it will overflow while being perfectly clean. The first place to look is below a valley, where two planes hand their water to a single point that frequently has no more capacity than the straight run either side of it.

After, and it belongs in the scope rather than in an assumption. A tear-off puts granules, fasteners and fragments of old covering into every run beneath it, so a gutter cleaned the week before is full again by that afternoon. What matters more is that somebody checks the outlets and any buried discharge line afterwards, because that is where the debris settles and none of it is visible from the top of the gutter.