No. It does not matter in every day code. Note that the stack you have linked to specifically addresses ditching that method in favour of the .net 4 implementation.
The Capacity of a StringBuilder
dictates the initial size of the underlying buffer. This buffer will expand as needed - I think it simply doubles in capacity each time it needs to grow.
StringBuilder.Length
keeps track of how much of the buffer is valid (assigned)
data. Capacity and Length are independent.
Capacity
is an optimization feature. By zeroing the capacity, all you are doing is ensuring that a memory allocation will have to be performed if you add characters to the StringBuilder
in exchange for reclaiming that buffer straight away. It is a classic tradeoff.
Rarely do you need to complicated your code by modifying the capacity.