Inbound scans are typically systems which are trying to connect to file shares that might be available on your system and hence these should be blocked. While most of this traffic is the result of worms or viruses which can use open file shares to propagate, they also can be the result of malicious users attempt to connect to your computer. Once connected they can download, upload or even delete or edit files on the connected file share. If you use open file shares (including sharing of printers, etc) on your local network (LAN), then you should be using a firewall such that your local file shares are not accessible from the internet. Connecting to open file shares is likely the easiest and most common hack on the internet and yet one of the most effective for malicious activities like identity theft or installing RATs (Remote Access Trojans) to take control of systems remotely for example.