Years ago I bought a very charming mid-century modern rancher with post and beam ceilings. Off the living room was a large space with tall windows on three sides and a plastic corrugated roof - so it was full of light which was great, but unheated so freezing in the winter.
The house was built in the 1960's and it appeared that some owner had enclosed a covered porch in order to have more interior space. I had dreams of redoing the badly done reno by installing a proper roof, updating windows and putting in a new heating system - all to be done by a professional contractor. Now some contractors may do a great job without obtaining permits (permits can take months to obtain from your local municipality).
However there are risks to not obtaining the appropriate paperwork. Firstly, when you go to sell your property, you must disclose that alterations were made without permits because that is considered a material latent defect. Often unpermitted work will affect the sale of your home in some way. Secondly, if you are not selling but are planning to do further renos that require permits and you apply for the permits, the city will come to inspect the work and may notice the non-permitted work, which MAY have to be undone or redone at a considerable cost.
For more details on permits, visit: