Working on both personal and commercial projects, I feel I can comment on both sides of the spectrum.
Teams usually work best in a business setting. A company hires you to work alongside other talented people and you are all given a project (or multiple usually) to work on and to have completed by the deadline. While your input is allowed, you generally are just fulfilling the needs of the project manager. You are being paid to help complete their project so you all generally have the same goal, see this as your full time job (because it is), and are being compensated appropriate payment (hopefully).
When teams work well, you get a lot of work done you yourself wouldn't have been able to get done otherwise especially with deadlines knocking around the corner. You also have the ability to fall back on others for help if you are struggling with a problem. Almost always in a well formed company, somebody will usually have an answer or at least be able to help you find it as you will generally be working with people who have been through many years of the development cycle and jumped through similar hoops.
That isn't to say teams don't have issues. Even if you are working with other talented members under a company name, you still have communication issues as well as interpersonal issues. Generally with practice, you can get better at these and having good team leads or managers really help bridge some of these issues. One thing I have seen is people working in teams are thinking more about their own needs than those of their team members and the needs of the project. Therefore, when something goes wrong, it is very easy to point fingers at someone else instead of just learning from the mistakes and moving forward.
When it comes to personal projects that are not your full time job, you simply just won't give it as much attention. When you ask other people to help contribute, because it also isn't putting food on their table and they have other obligations, your project becomes a lesser priority as well. You can always contract people (you should contract over hire if you aren't bigger than a small company in my opinion) to do work for you, but you want to be far enough in your project that you can provide a thorough list of what you need and to be specific for any changes/kickbacks you require as well. Not doing so will only cause headache for everyone.
Since most people here obviously are working on personal projects (that may or may not be sold) and usually can't afford to contract other people, the best option is to do as much as you can by yourself and keep project scope in small chunks. If you have to get help, I would only dump the amount of money on the project that the project itself is worth. In other words, don't hire a 20 year professional to provide high quality art for your 15 minute RPG, but on the flip side don't ask random Joe on the internet to contribute to a really serious project where the risk of him/her not working out is too high.
If you ask hire or ask others to contribute, you will have to practice your communication skills (people don't know what you want), have a solid plan, and be very versatile and adaptive when things don't go the way you expected them (and they never will).
All in all, if someone really isn't working out, get rid of them sooner than later as otherwise you'll only be hurting the project more and more both with quality and team morale.
Hope this sheds some light.