Recently I tried a tutorial. In that, they used the resnet50 from torch.models.
model = models.resnet50(pretrained=False)
for param in model.parameters():
    param.requires_grad = False
    
model.fc = nn.Sequential(nn.Linear(2048, 512),
                                 nn.ReLU(),
                                 nn.Dropout(0.2),
                                 nn.Linear(512, 256),
                                 nn.LogSoftmax(dim=1))

Can someone please explain what happens here? They are not using a pre-trained model, then what will be effect of requires_grad = False?