character class vs capturing groups

C:\Users\Regex\Desktop\dev>pcretest -m -t
PCRE version 8.34 2013-12-15

  re> ~[abc]~g
Compile time 0.0010 milliseconds
Memory allocation (code space): 40
data> abcdefghijklmnopqrstuvwxyz
Execute time 0.0002 milliseconds
 0: a
Execute time 0.0001 milliseconds
 0: b
Execute time 0.0001 milliseconds
 0: c
Execute time 0.0013 milliseconds

C:\Users\Regex\Desktop\dev>pcretest -m -t
PCRE version 8.34 2013-12-15

  re> ~(a|b|c)~g
Compile time 0.0015 milliseconds
Memory allocation (code space): 27
data> abcdefghijklmnopqrstuvwxyz
Execute time 0.0003 milliseconds
 0: a
 1: a
Execute time 0.0003 milliseconds
 0: b
 1: b
Execute time 0.0003 milliseconds
 0: c
 1: c
Execute time 0.0033 milliseconds

C:\Users\Regex\Desktop\dev>pcretest -d
PCRE version 8.34 2013-12-15

  re> ~[abc]~g
------------------------------------------------------------------
  0  36 Bra
  3     [a-c]
 36  36 Ket
 39     End
------------------------------------------------------------------
Capturing subpattern count = 0
No options
No first char
No need char

C:\Users\Regex\Desktop\dev>pcretest -d
PCRE version 8.34 2013-12-15

  re> ~(a|b|c)~g
------------------------------------------------------------------
  0  23 Bra
  3   7 CBra 1
  8     a
 10   5 Alt
 13     b
 15   5 Alt
 18     c
 20  17 Ket
 23  23 Ket
 26     End
------------------------------------------------------------------
Capturing subpattern count = 1
No options
No first char
No need char