Windows (and OSX) make it quite easy to share directories and files with other people on the same network. Which is all very well, but if you move to a different network those shares may no longer be appropriate.
As an example, imagine you share a directory containing family photos and videos so that your family can grab copies of them. And then you take your laptop into work; all those photos and videos are visible to anyone using the same wireless access point you are using. There is of course the reverse – you could be intentionally sharing some work documents with your colleagues and unintentionally also sharing them with your family when you take your laptop home.
In the first case, it is your decision on whether you want random strangers to see your family photos and videos. However in the second, you should really not be using shares on your laptop to share documents at work. There are plenty of other options for sharing documents – the K drive, the EDM system, Google Docs, etc., so there is no real need for turning on file sharing.
If you want to disable sharing :-
You can set up sharing so that it is only enabled on a “Home” network, but that looks to be quite complex so you may have to spend some time working out what gets enabled and where.