Opinion is split on this one. The traditional view is that high BG is ok as long as it doesn't stay there too long. And it is the average BG that is really important. It is based on findings from big studies like the DCCT. But more recent research suggests that BG spikes are in fact harmful.
My experience has been that when BG spikes, getting it down again can be really difficult. And overcorrecting invariably results in hypos. Matching carbs with insulin action, to my mind, is more trouble than it is worth. I avoid spikes by limiting carbs and bolus insulin simply because removing BG volatility simplifies my life.
