The TOC component generates header element id attrs based on the header text.
Here’s a header for example.
main outlet
The spacing comes from the styles applied to #main-outlet, which is a Discourse app element having nothing to do with this post.
This isn’t the end of the world if I could specify an alternative id for the header. The TOC component supports this:
https://github.com/discourse/DiscoTOC/blob/master/common/header.html#L293
Unfortunately, Discourse removes id attrs from post elements before the above code is run so the logic is thwarted.
Here’s a header that uses <h4 id="alt-main-outlet">main outlet</h4>:
main outlet
Note that it still uses main-outlet rather than alt-main-outlet.
I guess Discourse does this in anticipation of someone hacking a page element. But with the TOC component this is easy enough to bypass.
If there’s a solution to this or this is otherwise a well discussed problem that I’ve missed, apologies for the unsolicited opinions that follow 
P.S.
Personally I think Discourse should NOT strip element id attrs. This is a fundamental web page construct and is used in page navigation with URL fragments. If someone wants to create a link to an element in a post, I think that’s their right as an author.
The fact that TOC opens up ID hacking suggests that this measure of stripping IDs in the first place can potentially be dropped.
If the Discourse team is that concerned about ID hijacking, all Discourse IDs should be prefixed e.g. discourse-main-outlet and ID stripping should apply only to those prefixed IDs.
I can appreciate the impossibility of this given existing code!
One can imagine a set of excluded IDs (e.g. main-outlet, etc.) that are stripped. This still leaves the problem of TOC being used to bypass this safeguard but it would at least let authors create useful anchors.
P.P.S.
Directly related to this is the problem of headers with the same text payload.
Topic One
Examples
Topic Two
Examples
With TOC, both Examples headers get the same ID, which is obviously quite broken. TOC could append incrementing indexes (e.g. examples, examples-2, etc.) — and it probably should as a default course — but still better would be a solution to the problem discussed above, which lets authors decide how to describe their content. E.g. <h5 id="topic-one-examples">Examples</h5>, etc.