The advantages and disadvantages are as follows :-

Until the offer is accepted the offer can't be said as complete so it provides a security which brings the attention of the contract into existence at the moment of acceptance.

Advantage of it is that when the offer of acceptance is being made and the receiving party sends the confirmation to the party which sent the offer than the offer will be considered as valid.

The disadvantage of it is that the offer can be terminated or rejected on the part of the person who is offering the offer. So it is totally dependent on the offerer rather than the the person who is involved in it.

Another disadvantage of this is that if the offeree rejects the offer then offerer can't be accepted at future time