It varies greatly depending on the campaign. Though I will generally rule out the idea that a whole town or city would be considered the home base. The home base would merely be a location within said town/city such as a particular tavern or inn or maybe even a distinct neighborhood. That being said, home bases in my games are never sacrosanct and are included in the things that I will mess with as a GM. The PCs ship might get stolen, the inn may burn down, or the city containing the home base may be cut off during a seige. I do enjoy having PCs with a "base of operations" as it helps tie the PCs to the setting, and allows the use of recurring NPCs, to a greater degree. Unless of course the PC home base is mobile, but that can be made a secondary feature by having the mobile base have a "home port" as it were. I did that alot back in the day when running Star Wars D6. The party almost always had a transport ship as their default home base, but I would often feature a specific port of call as being particularly safe for the ship to reside when the players needed a break from the action. Then, while the ship remains the defacto home base, the port becomes a secondary one where recurring NPCs reside.