Avoid if you can. A lot has been written about this topic across social media including result of lab tests. The reality is that you can’t equate real life circumstances to a manufactured test environments.
First of all, the battery has a certain life. In general mobile phone batteries, the number of times of charging and discharging is about 500 times, and one charging cycle is calculated according to charging to 100%. Therefore, while charging while playing the phone, the charging cycle of the phone will be reduced. The biggest problem when playing mobile phones while charging is that the battery of the mobile phone is prematurely aged, and the cost and frequency of replacing the mobile phone battery are increased.
In addition, today's mobile phones have fast charging functions, but generally use high power to achieve fast charging. There are also some low-voltage fast-charging mobile phone products, which have high charging efficiency, fast charging speed and low heat generation. However, because the low-voltage fast charge has higher requirements on the charger and the charging line of the mobile phone, the high-voltage fast charging scheme is used more, which also inevitably causes the heating phenomenon of charging.
There’re always multiple others practical usage risks like.
1. Increased radiation. Cells get excited when being charged. They become warmer and emit more radiation. May be tiny for a smartphone but, little drops of water from a leaking tap will fill up a bucket soon enough.
2. If your charger or usb cable is fake, risk of fire is higher.
Most of the Smartphone batteries today are made up of lithium-ion so the biggest problem with them is over-charging but it's heating even the heat of your body is enough to help kill a battery quicker.
So now, if you use your phone continuously while charging on a regular basis then these following things can happen:
A. Short Term Damages:
Your phone will start heating up quite a bit.
Performance may get affected.
The touchscreen can go a little errant while you try to touch the screen.
B. Long Term Damages:
The life cycle of the batteries will go down ie after a year or 2 you won't get the same the same battery performance as before (all batteries degrade over a period of time but in this case it would degrade even more prominently).
C. Your battery can swell and after a certain point it will possibly be dangerous to keep that battery. Check out this link to avoid swelling:- What to Do When Your Phone or Laptop Has a Swollen Battery.
D. Permanent Damage: Your battery may explode but note that, this is a rare occurrence and batteries explode from various other causes too.
Suggestion: Avoid using your phone while charging or else just do lighter tasks while charging and no gaming.