It is okay to keep the AC adapter plug in while in use.  Newer laptop has Adaptive power management, it learns the usage pattern to adjust the charging mode and optimize battery health.  Battery life is averagely about 300 charging cycles.  Avoid a complete discharge of battery, it will shorten its life.
I just bought new Inspiron 3501. May i know that i should use power adapter while using with 100% full at battery and noticed that light for charging is off. Is mean no charging to battery and laptop is using from power adapter? thanks in advance. 
Request for Advice for inspiron 3501