In addition to mapping my locations, giving my characters streets to travel on, I also map their homes, places of business and so on. I use floor plans that I have found on the internet. I have a collection of floor plans of public buildings, various houses, apartments and even recreational vehicle floor plans. These only give me the layout of the home that I have chosen for my characters to live in and the places where they work. That’s all they are intended to do. I have to mentally decorate and furnish the rooms, but I know the layout of the rooms.
A floor plan can keep things natural. Unless your character lives in a TARDIS (from Doctor Who), rooms do not disappear when not in use. You need to remember the layout of the place where your characters live. A floor plan will help you do that.
You could draw your own, or you can find one that you like on the internet, either method is fine. I can’t draw so I look online for images that I can use to help me visualize the building’s layout. Then you just have to keep it handy while you are writing your story because it wouldn’t do to change the layout of the building unexpectedly. Unless they are ghosts, your characters can’t go through walls. Readers have sharp eyes and they will spot discontinuities like that. A floor plan can keep you consistent. Consistency is important.
Floor plans are tools that you can use to give your characters places to live and work. I find it helpful if I can say that a character has to turn right to go downstairs in their home from their bedroom and be able to keep it consistent. The floor plan is a reference tool. It makes it easier to remember the details. The details can trip you up and having a floor plan of the building will help you keep the details straight.
If you map your world, you should also map out the buildings in the world. It doesn’t have to be to scale. After all, you aren’t actually building it, unless you are into making models of your locations. You just need to know the layout of the building so your characters can move around it easily. It’s something simple enough to obtain on the internet, or you can simply draw your own on a piece of paper. However you do it, a floor plan can be a good tool for visualizing where your characters are during the action. That’s the important thing. If you can’t visualize where your characters are in the story, your readers won’t be able to visualize it either.