Re: What does limit ad tracking mean and should I set it on or off?
As per Apple - How to opt out of interest-based ads from iAd
To give you the best advertising experience, we recommend that you keep Limit Ad Tracking turned off on your iOS device, Apple TV, and iTunes desktop client. If you don't want to receive ads related to your interests from iAd, you can turn Limit Ad Tracking on.
Long story short, Apple wants to send you ads it thinks you may like. If you don't want those ads and just want more generic ads turn it ON
On your iPhone, you can go to: Choose Settings > Privacy > Advertising.
If you've turned on Limit Ad Tracking, you can restore interest-based ads by turning Limit Ad Tracking off.
Note: You must be logged in to iTunes for these settings to apply to your account. We also recommend that you restart iTunes Radio for the Limit Ad Tracking setting changes to take effect.
By opting out:
You may see the same number of ads as before; however, they may be less relevant because they won't be based on your interests.
You may see ads related to the content in an application or based on other non-personal information.