There are many ways to win the game of poker. One of them is blind steal. If everyone else folds when we raise, we will win the money regardless of what cards we have and won't even have to see a flop. What cards we hold doesn't matter; we can be a lot more aggressive with weaker hands than we normally would be. The times we win, we've been conservative. In fact, we'll often win more than that, since others won't always fold post flop with the worst hand. There are people who play very well out of the blinds and they know that we rise with weaker hands from the button than we do from an early position and will adjust accordingly.
Good players can be straightforward and bad players can be tricky. It is good to play against the straightforward kind rather than the tricky one because with the bad tricky player, we can lose control and make mistakes, which is not likely to happen with a good straightforward player. If we've decided that our player in the big blind is good and tricky, it's fairly safe to simply ditch in the cut-off, but if we're still borderline, we can look at how aggressive or passive our opponent is. This is not going to change how many hands we steal with, but rather which ones we try it with.
The closer we get to the point where we should be raising for value, the less we mind if someone will call. So while we can steal with any two cards, we should always raise when we're opening the betting in late position. If the players in the blinds are really bad post flop, we should call for one bet with medium strength hands. Since they're unlikely to fold anyway, we should prefer to keep our own investment before the flop and use our skill to make better decisions than them after the flop. The reasons that exist to bet or raise in poker includes a better hand may fold, a worse hand may call, not everyone folds, but you get last position, you are already in last position or choose to take a free card on the next round.
There are very few exceptions for when we should not bet heads up when we've steal raised before the flop. Some people slow play really big hands like flopped sets because they don't want to drive them out. If the big blind has some piece of the flop he won't fold for a continuation bet or he may check raise us. The many bets that will rarely win if our slow play succeeds combined with the stray bet that we pick up from failed turn bluffs don't normally make up for the many times we win a small bet by simply betting the flop. When we're up against thinking opponents, we will get check raised on the flop both with weak hands and sometimes with pure bluffs.