Is it recommended to keep the charger connected all the time?

You can leave the charger plugged in whenever convenient to do so. Leaving the charger plugged in will not damage the battery or the computer. Leaving it plugged in will reduce the rate of accumulation of battery cycles. Modern operating systems manage the power and battery on Macs.

There is no issue if you do keep it connected. The Mac will manage its charging and cannot be overcharged.