When you have social media pages, chances are that you are focusing on developing one at a time. You are, then, building your Facebook followers on your Facebook page and are likely growing your Twitter page through the use of your Twitter page. While this is great, it is not as effective as it could be if you linked your accounts and strived for cross-promotion. There is nothing to say that you cannot promote your SnapChat account on your Twitter page and your Facebook on your SnapChat account.
What is great about cross promoting your business is that you can grow your free followers and your free likes exponentially. That is to say that you can really build your following by pulling your followers from one account or group into the next. As such, you need to make sure that you are utilizing your social media pages to the max potential by using the tools of cross-promotion to the best of your ability. If you do this, then, you are likely to not see one page decrease in its followership as another goes up. You will likely see both pages or more go up in their followership and likes count as you cross-promote.