The small footprint and low energy demands of Raspberry Pi make it ideal for remote deployment, and accessing Raspberry Pi from another computer is a common user request.
There are many different solutions for remote access to Raspberry Pi. The most common is to use one of two techniques: SSH and VNC.
SSH and VNC involve opening a port on Raspberry Pi (VNC uses port 5900+N and SSH uses port 22). This potentially exposes your Raspberry Pi. Hackers actively look for Raspberry Pi devices with these open ports and default passwords. This is why you must change your password when turning on VNC.