I see it as @SimonW.
It won’t cause an error, but you will most likely get the same batch over and over again.
Have a look at this small example:

class MyDataset(Dataset):
    def __init__(self):
        self.data = torch.arange(100)
        
    def __getitem__(self, index):
        return self.data[index]
    
    def __len__(self):
        return len(self.data)

dataset = MyDataset()
loader = DataLoader(dataset,
                    batch_size=1,
                    shuffle=False)

data = iter(loader).next()
print(data)
data = iter(loader).next()
print(data)
# Prints 0s every time

data_iter = iter(loader)
data = data_iter.next()
print(data)
data = data_iter.next()
print(data)
# Gets new batch (0, 1, ...)