There might be a difference, if you were resetting the default CUDA device via torch.cuda.set_device() as seen in this code snippet:
torch.cuda.set_device('cuda:1')
x = torch.randn(1).cuda()
print(x)
> tensor([0.9038], device='cuda:1') # uses the default device now

y = torch.randn(1).to('cuda:0')
print(y)
> tensor([-0.7296], device='cuda:0') # explicitly specify cuda:0