Capturing a snapshot is not "free" obviously, but 30mins typically is no cause for concern, and my personal experience has been 1hour tends to smooth things out too much. If you have a disaster for 15mins, but the other 45mins is fine, the whole hour tends to look "OK"

In particular, I've also known of customers who have gone to 5 or 10mins for particular performance analysis with no major issues, ie, they run at (say) 20mins, but if they want to track a particular time frame that is critical, they'll bump it to 5mins for an hour or so, and then back out to 20 or 30 when done.

Obviously more snapshots means more space etc...so common sense is always the key here.