So we have 2 options to make ints positive: 
1) zigzag
2) subtracting the minimum value.
I prefer the second as it will use less bits in bit packing.
example:
Say min value is -1 and max value is 6
1) zigzag gives a max int of 12 which fits on 4 bits
2) adding min gives a max int of 7 which fits on 3 bits
Similarly if min is -6 and max is 1:
1) max: 13 => 4 bits
2) max: 7 => 3 bits

zigzag would be useful if we want to encode ints in a var_int scheme without doing delta. (say the values are more uniformly distributed)