" When is it useful to use mirror? "
- If you can imagine placing a mirror along one half of an object, and the object appears correct, use a mirror.
- Even when the geometry on both sides is mostly mirrored and differs slightly, you can edit each side individually after applying the mirror (breaking the symmetry).
For anything with symmetry:
you can mirror x,y , try it! place the origin at the center and tick both x,y axis for the mirror.
Array Modifier can be useful when the repetition goes beyond straight x,y mirroring. Use an empty as the
object offset and rotate the empty on (for example) the z-axis by 60 degrees, to get a
radial array like this example:
object offset is generally referred to as the
pivot point when talking about radial arrays.
And then there is the
Screw Modifier, which can be considered a
Lathe modifier, which lets you draw a profile and rotate it around to form the shape. This is very common practice. I prefer the screw modifier instead of the
Spin tool, because you can keep editing the profile without having to 're-spin'
You can combine these geometry modifiers, for example you can mirror a section then radial array the result. Here's a crude example