I use the safety a ton myself but I rarely, if ever, run the stock defenses like they are diagrammed. Being intimately familiar with man coverage (75% of my defense) I use my safety to compensate for wherever my coverage is weakest - usually in the middle.
I use my safety to help disguise my coverage. I FREEZE the defense and manually shift/move players based on my opponent's formation and motion usage. If a receiver is moved to a position where he is uncovered, I move the safety head-up over him to give the illusion that the safety is responsible for the coverage (sometimes he actually is).
Regarding Auto-Strafe and Auto-Sprint... NEVER. I turn these OFF before ever starting a game. If you're like me, you don't trust the CPU enough to know when it should strafe and sprint. I NEVER let the CPU do what I can do manually.
I blitz from the safety position rarely. About once every 3-5 games, but it depends on my opponent and his play style. If he's susceptible to pressure but I can't get to him, I'll bring my safety. I'll also manually blitz if my coverage is holding up well but the pressure isn't reaching the QB.
Whatever you do though, try to stay conservative on run plays. I find that my most disappointing performances occur when I'm too eager on off-tackle runs.
Later