Imagine you see a bat flying out of your attic. Now, one little bat may not be a bad thing. They eat bugs and it's kinda cool. True, they carry disease but it is just one.
So, you have a decision....hire a pro to do a bat exclusion...spend $1000 to seal up the entire outside of the home (they can enter through holes the size of a quarter) and then you're done. Or...take your chances and enjoy the fun at dusk of watching the bat fly away.
One of three things will happen: your bat problem will grow to three bats and you'll get a small guano/disease problem in your attic costing $5k to remediate, you will wind up with dozens of bats and a very big guano/disease problem costing $25k to remediate and you'll have to live in a hotel for a month, or the attic needs to be cleaned down to the studs or you may need to rebuild the attic and remove the soiled wood and your granny may need hospitalization due to respiratory problems.
Taking action early lowers your future costs, but it has a major upfront cost. Further, it is possible your bat problem doesn't grow to ginormous proportions...there is no guarantee as to where the bat infestation will go. Wayne Allen Root put it best:
I have many great friends and guests on my national TV and radio shows who are medical experts. Half believe this is the pandemic to end all pandemics. They quote Centers for Disease Control and Prevention models that report as many as 1.7 million Americans could die. So people are rightfully scared out of their minds. American business is shutting down. But the other half of my medical friends and expert guests say this is an overreaction. They predict fewer Americans will die than during the flu season of 2017-18 that killed about 80,000 people. They don't believe we need to close down American business and lock ourselves in our homes. The problem is we won't know who's right until it's over.