Yes, you can keep your external hard drive connected all the time. However, you should be aware of a few potential risks. First, if you leave your hard drive connected and powered on, it is possible for data corruption to occur. This is more likely to happen if there is a power outage or if the hard drive is bumped or jostled. To avoid data corruption, it is best to disconnect your hard drive and power it down when you are not using it.
Another potential risk is physical damage to the hard drive. If the hard drive is left connected and powered on, it is more likely to be damaged if there is a fire, flood, or other disaster. To protect your hard drive, it is best to disconnect it and store it in a safe location.