An executive agreement does not require a 2/3 vote by the Senate and therefore without Congressional approval an agreement can be reached more quickly.
An advantage of an executive agreement is a quicker process for reaching an agreement with a foreign power. In a situation where violence could or is occurring, an executive agreement could be necessary to resolve the situation.
A disadvantage is a lack of Congressional support. A treaty needs a 2/3 Senate approval showing the people and another branch of the government are supporting an agreement with a foreign country. If Congress does not get a chance to support the agreement, it may be difficult to create laws or provide money to the agreement when it goes into effect.
An advantage is that it takes way less time to do it than to create a formal treaty since the President would not need consent from the congress for an executive agreement. A formal treaty can, however, last longer because it is more difficult to cancel, so if it's good, then it is also safer for it to be formal.
