If your company can sponsor a charity event, PSA's are a great way to promote your company in a positive light. Most media are required by licensing agreements to provide a certain amount of time or space for the good of their local communities. Some of the downsides of PSA's. PSA's are often placed in off times. I don't want to paint everyone with a broad brush here.
Some media are better than others.
Just because you request a PSA, doesn't mean you'll get it. Media has a limited amount of space or time for PSA's. You might get a break if you are currently advertising in the media of choice. It might also help if your organization buys a small amount of time or space to run with your PSA's. The Last Word On Types Of Advertising The type of message and your target market will often dictate which type of advertising to use.