Using the mirrors at the gym in Oasis Springs as an example, starting with the 3 panel wall mirror you have 2 seams in your wall mirror.
![](http://i832.photobucket.com/albums/zz247/grimsoul_bucket/The%20Sims%204/gym%201.jpg)
Now turn on the moveobjects cheat and get the single panel mirror and place it so it is over one of the seams to hide it.
![](http://i832.photobucket.com/albums/zz247/grimsoul_bucket/The%20Sims%204/gym%202.jpg)
Now just do the same thing for the other seam and you now have a wall mirror with no seams showing. Which I think looks much nicer.
![](http://i832.photobucket.com/albums/zz247/grimsoul_bucket/The%20Sims%204/gym%203.jpg)
You can make any size wall mirror you need by using a combination of the 3 panel and single panel mirrors. Like if you just want one that is two panels wide place two of the single panel mirrors side by side and place a third one in the middle to cover the seam.