Help with focus limiter on Sigma 150mm macro

I have an older model Sigma 150mm macro lens, no OS/VR, that I recently purchased used.  The image clarity is great both for macro and regular images.  However, I still have not been able to figure out how to properly use the focus limiter.  Currently leave it on full and manually focus.  When should I be using the other limiter settings?

Here are a couple of examples of images I have taken so far - nothing spectacular, but just learning.  Also, spring is just starting:

Leaf buds on Variegated Wiegela bush

Flower? in moss on a rock

Susan

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GreenMountainGirl