The highest possible target (difficulty 1) is defined as 0x1d00ffff, which gives us a hex target of
0x00000000FFFF0000000000000000000000000000000000000000000000000000
It should be noted that pooled mining often uses non-truncated targets, which puts "pool difficulty 1" at
0x00000000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
From what I know, using non-truncated targets puts the target at a higher number than the network would accept. In other words, we may end up finding a hash accepted by the "pooled mining" (lower than non-truncated), yet rejected by the network (higher than truncated).
Why do people use non-truncated mining targets?
Why not simply use the actual truncated targets so that we can have a more accurate picture of the network and avoid overheads incurred as such?