What will I lose functionality of if Usage Sharing is turned off?

I turned my usage sharing off and nothing happened no frame rate losses or graphics issues. It is the game wanting to get data from players on time played or other stats.

Speaking from someone rather aware of the development process for this type of software...

In general, when creating software that is massively used like this, there needs to be a way to make sure that broken pieces get fixed. This is most likely what this data ensures.

Disabling sharing may result in loss of functionality

Keyword here is may. While some data may be in relation to where users travel in game, and what they use to try to balance encounters, the portion of data collected pertinent to functionality is going to be things which cause internal errors to be logged.

This data is collected in order to track bugs so that minutia which most users probably miss, and essentially none report, can be fixed in subsequent patches.

Without sharing this data, there will be no way to guarantee bugs which effect your specific environment will be noticed. Moreover, there will be no indication of representation for your specific environment during testing.

As a result, without this data, it is possible that your environment may suffer random side effects due to either not being fully tested or due to errors not being fully noticed.

This notice is more of a warning that future patches may introduce breaking changes for your environment without the inclusion of data they deem important to quality assurance.

While it is highly unlikely there would be an issue either way, it certainly helps to maintain the quality of the overall game by sharing it. If there were to be any loss of functionality, it probably wouldn't be for quite some time.

IT IS UNFORTUNATE THAT THEIR MESSAGE IS SO VAGUE. IT WOULD BE BETTER IF IT WERE MORE TRANSPARENT.