(This is today's bit of advice from the book Safety Toolbox.)
In the course of a game, you have many opportunities to perform cross-side, cross-corner, and long-table banks. Bank shots are usually not high percentage. Unless you dedicate a major part of your shooting career to playing Bank Pool, these shots are not consistently dependable. Even excellent players are happy with a success range of around 50-65%. This level of competence is still not enough to constantly depend on them.
When facing a situation where a bank is one of your options, first calculate the chances of success based on your skills. This is not a time to fantasize perfection. If you have not devoted significant practice time, attempting a bank shot is an excellent chance for your opponent to come to the table.
Assuming that banks are naturally untrustworthy is a good starting point. Working with that as a basic standard for all banks, you can turn an iffy possibility of success into a guaranteed result. Play the shot, not to make it, but to setup a defensive effort. This is easily done and provides the opportunity to send the cue ball away at the same time. When considered this way, using the bank to actually play a safety makes a lot of sense.
The secret to turning a bank into a defensive shot is speed control of the object ball. Sending the cue ball away is simple with some helpful spin to make it travel even further.
In 8 Ball, an apparent bank attempt should have only enough speed to leave the object ball close to a pocket. That ball can be picked up later as an easy shot. Once the correct speed is selected, analyze the various options available to a side-spinning cue ball.
For 9 Ball, an apparent bank attempt can ensure that the object ball dies exactly where you intend. On a cross-corner shot, it can be stopped in the middle of the dead zone. Appropriate cue ball spin ensures a tough distance/bad angle safety. If your opponent raises an eyebrow at the shot, shrug sheepishly and apologize for giving him a bad shooting opportunity.
And don't forget the benefits of sending the object ball two or three cushions in a seemingly stupid attempt at a multi-rail bank. These can position an object ball into a good location for your next shot at the table. It also hides your clever planning ability (and ball control skills).