Why is it better to wrap transactions inside a using block?

[adam.krug]

I read here and there on the net that it is always better to set up a transaction like below:

using (Transaction  tx = new Transaction(doc, name))
{
 tx.Start();
 some stuff here
 tx.Commit();
}

The alternative is like:

Transaction tx = new Transaction(doc, name);
tx.Start();
some stuff here
tx.Commit();

What is the reason the first is better than the latter? Or you have a different opinion? Please share.

[cwaluga · Accepted solution]

The Transaction class implements IDisposable, so it is just a matter of controlling when unmanaged resources are released.