You should figure out where you place your add.
It depends on what you´re doing.
At least it can be uncomfortable for the user - what means less fun and less happy users.
But be aware of the policies each ad-company brings with it.
For example AdMob:
The guidelines tell you what is a go-go or a no-go for several scenarios.
You can find also some videos showing/explaining what is necessary to pay attention.
Please inform yourself before you place just somewhere a ad-block and your account gets frozen or banned.
Link to the guidelines: https://support.google.com/admob/answer ... hl=en&rd=1