Do we need a prototype to file a patent and if no then what are the disadvantages of having a prototype?

No you do not need an actual embodiment. There is no disadvantage that i am aware of.

You do not need a prototype to file a patent application. I'm not sure if there are disadvantages of having a prototype, other than the cost if you are only making the prototype for purposes of a patent application.

You don't need a prototype to file a patent. Prototypes cost money and take time. If they involve other people then you are also risking disclosure of secret information. They are often helpful, though.

No prototype is required. Instead, you need a written description of (a) what the invention is, (b) how to make it, and (c) how to use it. Having a prototype may make you focus only on that particular version of the invention - made with what you had available or could afford. The written description is not limited by parts availability or budget - create (in words) the "ultimate version" of the invention. You can also discuss parts that can be changed, optional add-ons, etc.

A prototype is unnecessary to file a patent application. There are no disadvantages to having a prototype of the invention. When filing a patent application, the inventor only needs to possess a clear understanding of the inventive concept such that one of skill in the art could apply ordinary scientific and engineering principles to reduce the inventive concept to practice. While not required, having a prototype is useful when preparing and filing a patent application because it can be used as one of the exemplary embodiment described in the detailed description of the invention in the patent application. As always, an inventor is well-advised to seek the advice of a registered patent attorney when considering any aspect of intellectual property rights as applied to your particular facts.