Two types of people that you will come across:
1. The person that is always "busy" and uses it as an excuse for not getting things done.
2. The person that has a mediocre level of performance but sticks around because they are a "nice guy" or girl.
There is nothing wrong with being busy. Many of us are. But if you willingly add on multiple projects/responsibilities and do a poor job of managing them, you are doing a disservice to yourself and others. Or you will find people with loads of free time that hide under the "busy" label.
This type of person sets deadlines, fails to reach them, and uses the "busy" excuse to legitimately not get the work done. It is mediocre form and irresponsible to the other parties involved.
There is something to said about being a cordial, affable person. It is a positive thing. However, in the business world, it cannot replace competence.
I have fallen for this trap with the seemingly nice, incompetent person. You may want to stick up for them... "such a nice guy (or girl)."
But if the work doesn't get done, you are carrying dead weight. And some people lose competence over time. They may have done some great things for you in the past, but they have to be let go. Easier said than done when you have made an emotional connection with them.
I have also seen many conniving, manipulative people wear the nice/affable mask. When you spot someone like this, distance yourself and take them out of the equation if possible. Remember to keep your hands clean.
Hold busy people accountable and don't work with incompetent "nice guys".
A post from Sebastian talks about a related topic, friendly and polite:
"Someone being friendly to you is: Looking out for your interests.
Someone being polite to you is: Obeying social decorum.
People are very often highly polite and highly unfriendly at the same time.
The opposite way is greatly enjoyable and profitable."