Answer
Why does pointing matter on a patio?
It keeps water out of the joints and bed; good pointing is what makes a patio last.
In short
Pointing, the filling between the slabs, keeps water out of the joints and the bed below, which is what stops a patio lifting, cracking and growing weeds. Done badly it fails fast; done well with the right jointing compound it lasts. It is a detail that quietly decides how long a patio lasts.
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