Until not too long, psychologists had difficulty understanding human behaviours. Psychologist largely employed the scientific process or the use of empirical evidence to study and understand human behaviours. The big five personality traits were discovered in the late 20th century.

Agreeableness is one of the big five personality traits. Agreeable people are polite, empathetic, compassionate, conflict-avoidance, lack good negotiation skill etc.

One way of conceptualizing it is that agreeable people fit well in a group function, the are the best kind of people to get to work in an organization as they exhibit positive behaviours, it's a pro social behavioural trait.

You might want to know if you are agreeable or not. Agreeable people:
Are polite. Polite people are well mannered, courteous, respectable, civil, gentlemanly, and ladylike. If you are approachable, does not gossip, listen to what others have to say, and do not judge people, you are very agreeable.
Are empathetic and compassionate. They are very sensitive people who are quick to understand people's emotion and can go out of their way to help them. They let themselves to be moved by the suffering of others and motivated enough to help them.
Are conflict-avoidance. They do not like trouble, they would rather let you have your way with them than engage you in a fight.
Are not good at negotiation. The more agreeable you are, the more likely you are to negotiate on the other person's behalf.

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Well, agreeableness seem to be a good social behavioural trait, on the individual level, it might not be good to be too agreeable, as:
Agreeable people are often resentful: there resentment Is often rooted in their inability to be very assertive: articulating what you want and sticking to it without being able to be subtly manipulated out of it.
Agreeable people are often exploited because they are compassionate, empathetic, and polite(emotional), they do not know how to negotiate well and always want to please others.
Agreeable people cannot stand up properly for themselves, they often rather bend over backwards for others, they do not know how to be necessarily selfish, they always have others best interest at heart at the expense of there own interests.

Conclusion

On the average, women are more agreeable than men, but that is not to say that there are not men that are very agreeable like women.
Agreeableness is a spectrum of two extremes with very agreeable people at one extreme and less agreeable people at the other extreme. If you think you are an agreeable person, shifting away from the extreme of agreeableness, especially when situations call for it, would be helpful.

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