Is there any Q10 deficiency?

Of course there is. There might be two reasons: the production is very low or too much is used.

There are 10 genes responsible for normal Q10 producing, if any of them works abnormally, Q10 level reduces. According to some studies, Q10 level reduces due to several chronic diseases, such as cancer, chronic heart disease, etc.
There are also some drugs which are able to inhibit the Q10 producing, so in these cases Q10 supplement is considered.

Q10 consumption increases in diseases, which affects more organs.
People obtain Q10 by food, but it is insufficient. In this case the supplement is very important.

Each cell of our body needs coenzyme Q10. The cells do not work and organs are unable to perform their function without energy supply. We may have learnt from the Internet, that in case of several diseases more Q10 is needed. Q10 will not cure the disease, but supports the cells and organs in their normal function, helping the patients during the hard times.
In lot of cases there is no sign of Q10 deficiency, but it is good for our body if the supplementation is ensured. It's much cheaper and easier to prevent illness than to treat it.