It isn't simply a matter of being picky. If the pencil lines are 1/16" wide, then you could be off by an 1/8" or more when you add up all the uncertainty. That may not seem like much but if your grip is already stretched, then 1/8" too much may be noticeable. An experienced driller shouldn't have any trouble with pencil lines but it takes a little more care to be consistent.
SH