Gelsenkirchen, Germany, march 19, 1945, the crew of medium M4 Sherman tank apply a layer of cement to the frontal armor of the tank in order to increase its stopping capabilities. View attachment 12489
For troops in the field neither of those questions would have mattered
A rumour/idea floating around that "might" increase your chance of survival, sure beats a concern that it "might" slow you down or decrease reliability. (Both of which "disadvantages" would increase your survivability by keeping you out of the front).
Another thought here is that by this point in the war the Sherman was underarmoured and very vulnerable to infantry weapons as well as guns - experienced crews would be both war weary and aware that they were driving around in vulnerable vehicles.
From the web: "....there is much debate as to the real protection gained by doing this & Gen.Patton was against it. He thought the added weight slowed the tank & therefore lost it's tactical advantage- speed/maneuverability. It certainly did provide a psychological comfort to the tank crews inside who used such improvised additions. Other crews added timbers & extra tank tracks outside the hull".....
Here, a Sherman crew member of the US 14th Armored Div adds a final flourish to cement filled sand bags on his tank.