Most of the time I've no particular destination in mind on a day cruise, so currents are largely irrelevant (except for determining turn-around time) and I may be moving 4.5 knots in one direction and 10 knots in the other because of the current. Tide levels can be important too: two hours before low tide we were "pushing mud" (with dredging overdue and chart soundings out of date) occasionally on the Petaluma River last Thursday. Nevertheless, tidal currents in the San Francisco estuary make a whale of a difference on one's forward progress.