Got this excellent answer from Reddit
The switch-mode power supply in the typical cell phone charger will use on the order of tens of milliwatts no matter what, because they are not perfectly efficient, and will constantly use some power to keep themselves switching when plugged in, providing the DC power your phone needs. Note that cheaper knockoff chargers, in addition to providing poor quality of power for your phone and being generally unsafe, can often be designed less efficiently than a branded charger and thus have a higher vampiric draw.
At the slightly above-average estimate of $0.20/kWh, using the upper bound of 0.100 watts, you can expect to pay a max of about $0.1753/year if you just leave an idle charger running. (If you want to check my math, $0.20/kWh = $0.0002/Wh => 0.100 W * $0.0002/Wh = $0.00002/hr => 8765.81 hrs/yr * $0.00002/hr = $0.1753/yr)
If it takes you 5 seconds to plug and 5 seconds to unplug your charger, for instance, you're spending just over an hour on this task every year. If we value your time at the US federal minimum wage of $7.25/hr, you're using ~4100% more time than it's worth.
So, in short, yes. You're wasting your time.
The switch-mode power supply in the typical cell phone charger will use on the order of tens of milliwatts no matter what, because they are not perfectly efficient, and will constantly use some power to keep themselves switching when plugged in, providing the DC power your phone needs. Note that cheaper knockoff chargers, in addition to providing poor quality of power for your phone and being generally unsafe, can often be designed less efficiently than a branded charger and thus have a higher vampiric draw.
At the slightly above-average estimate of $0.20/kWh, using the upper bound of 0.100 watts, you can expect to pay a max of about $0.1753/year if you just leave an idle charger running. (If you want to check my math, $0.20/kWh = $0.0002/Wh => 0.100 W * $0.0002/Wh = $0.00002/hr => 8765.81 hrs/yr * $0.00002/hr = $0.1753/yr)
If it takes you 5 seconds to plug and 5 seconds to unplug your charger, for instance, you're spending just over an hour on this task every year. If we value your time at the US federal minimum wage of $7.25/hr, you're using ~4100% more time than it's worth.
So, in short, yes. You're wasting your time.