Ethereum biggest weakness is the Nonce !

[CryptoGirl]

Read about what nonce is : https://www.altcoinstalks.com/index.php?topic=23937.0

But mainly, if your transaction 1 is not mined you can not send another transaction.
But, now with ever-growing gas price, transaction costs are no longer negligible !

thus unless you are ready to put a high gas price, your transaction will be stuck for few hours or maybe few days!

and during this time the account is useless, unless of course you want to increase the payment to make the transaction faster.