The Reality - There are many dogs who can sleep on a bed or sofa and never show aggression towards their owners or show any other behavioral problems. The act of letting your dog sleep on the bed does not mean your dog will begin to "dominate" your or that you will lose "alpha" status. Many of these ideas of dominance and being the alpha are questionable and it is more important to focus on the dog's behavior, your lifestyle and what you want in the long-term. See my article discussing the misconceptions of dominance in dogs.
My general rule of thumb is that pets on furniture is a personal choice if your dog is not showing aggression in this context. If your dog willingly jumps off the furniture when asked without growling or showing aggression, then it is generally not a problem. However, there are other considerations that you should take into account before giving your dog unlimited access to your sleeping areas.
I personally choose not to have any animals on my bed because 1) my large dogs take up too much space and 2) they are major shedders and I don't like having animal fur on pillows and areas where I sleep. My 12 year old shiba has sofa (but not bed) privileges as you can see in the photo above. However, she is still crate-trained and spends some time in a crate for meals and when I am training my other animals. In my case, it is a personal choice not to have some of my dogs on the sofa, but if people like having their dogs on the sofa or bed that is fine with the following caveats.
If you have a dog that is possessive or guards space, like sleeping areas, I would not give him/her unlimited sofa or bed privileges until the aggressive behavior is first dealt with. If your dog growls at you when you try to move him or when you get too close to her when she is sleeping then letting them sleep on a sofa or bed is not the best option. In such cases, it would be better to give the dog his/her own bed somewhere else and hire a positive reinforcement-based trainer to help you work through the aggressive behavior first before allowing unlimited access to your sofa or bed.
For puppies and newly adopted dogs, I recommend that you do not immediately give bed or sofa privileges until you have spent some time with your dog and get to know him/her better. I usually give it about 4-6 months for adults and a year for puppies. During this period you have worked through the destructive chewing phase, completed some basic training/manners training and you have determined whether there are any aggression issues or other behavioral issues such as separation anxiety that may impact where your dog should sleep.
After this period you can decide whether you really want to want a dog in your bed or on your sofa. For example, you may find out that your child has allergies, you plan on having a baby who will spend time in bed with you or you may realize after being with your dog that the fur on the bed is not your cup of tea. It is easier to give privileges than take them away. If you have been sleeping with a puppy in a bed from the age of 8 weeks, it is going to be much harder 8-10 months later to then try to train the puppy to sleep on the floor or in a crate. So when you decide where you want your dog to sleep, ask yourself if this is going to be o.k. with you in the long term with all the lifestyle changes your family will be going through during your dog's lifetime.