Mirrors can be your friends and your enemies both on the wall and in SolidWorks. If you’re making a part that’s symmetric, mirroring can save you a lot of time building matching features on both sides of the part. However, if you don’t do things correctly it can lead to lots of nightmares.
The biggest complications can stem from the base sketches of your part. Mirroring in a sketch is handy to create symmetric entities, but why not just mirror the feature instead? As a general rule, the more entities you have in a sketch, the more chances you’re giving your model to go wrong. Everything might be symmetric when you start, but if you go back in and edit something later it could all blow up.
Another headache can be due to how you’re defining your features. Mirroring “Blind” features is usually no problem. If you start using more advanced definitions like Up to Vertex, Up to Surface and the like the mirroring the feature may not work because it can’t find the appropriate geometry or extends to the wrong place to really be a “mirror.”
Some features like fillets and chamfers are really picky about the geometry they’re made with. If you try to mirror them, and the faces they’re being mirrored to aren’t exactly the same, they will likely fail.
There are so many ways to have issues! Why not just skip all of them? The solution: Mirror Body. Skip all the headaches of trying to mirror sketches and features and just model half your part, mirror the body and be done. Less sketch entities, less features and less hassle. If you want to ensure total symmetricity that’s your best way to go.