Castings usually aren't as strong as rolled plates, but (once you have the technical knowhow to make them big enough[1]) remove pr massively reduce the need for forming, cutting and welding all of which can reduce overall strength, create local weakpoints and take time [2].
[1] see Somua S35 for a good example of a decent cast tank that suffered from a one man turret. While political preference for the smallest possible crews played an important part, French casting technology though world class was about at its limit. Even if a two man turret was wanted, it may have been a step too far in the 1930s, and 1940 was too late. There was at least one French medium with a 2man turret but I'll have to check if it was cast.
[2] Big castings need carefully controlled cooling to avoid distortion, cracking and metallurgical problems like excessive brittleness or low hardness. It can take days to do properly, but the actual labour hours overall can be less than welding forming etc even if the total number of hours elapsed is the same.