Calculate garden hose water flow rate and fill time.
Hose flow is a pipe-friction problem, and diameter dominates it. Supply pressure is converted to head at 2.31 ft of water per psi, divided by the hose length to give the friction slope, and the flow follows a Hazen-Williams form in which diameter is raised to the power 2.63 while slope only reaches 0.54. That exponent gap is the whole story: going from a 5/8 in hose to 3/4 in raises flow by about 55%, whereas doubling the pressure raises it by only 45%. Length works against you in the same way — a 100 ft hose delivers roughly 30% less than a 50 ft one at the same tap. If you need more water at the far end of a garden, a fatter hose beats a booster every time.
Garden Hose Flow
Head = psi x 2.31 ft; slope = head / hose length; flow gpm = 40 x diameter^2.63 x slope^0.54; fill time = container gallons / flow
A 5/8 in, 50 ft hose at 45 psi runs about 17 gpm wide open with no nozzle. Add a nozzle or sprinkler and the restriction there, not the hose, sets the flow.
It reduces flow, which is what you notice. Static pressure at the closed end is unchanged; open the end and friction along the extra length eats the head that would have driven the water.