A Pot Hole uses "hidden" links, phrases linked to pages whose actual titles may not appear in the text. Tropes Are Not Bad. This is okay when done correctly, allowing links to relevant articles without disrupting the narrative flow.
Sinkholes occur when potholing goes wrong, featuring links that are irrelevant, inappropriate, or both. In a wiki, it's better to pot hole words which represent the article they are linked to. Here are some bad sinkhole practices:
... creates a sinkhole — the fact that he voiced The Joker is completely irrelevant to his role in Star Wars. More importantly, he has a page, so potholing his name to another page is odd. The reader has to maneuver around the sinkhole to avoid being knocked off track. It adds nothing to the wiki except the likelihood of confusion, as Hamill's page already provides readers with a list of his other roles, and clearly specifies that he voiced The Joker in Batman: The Animated Series (and other works), while the sinkhole only implies he has some kind of relation to The Joker. Such sinkhole links should be changed to point to what the text is actually about or un-linked altogether.
Chained sinkholes: These are when pot holes are chained with sinkhole characteristics. There's only one sentence, but many pages linked to. Instead of proper structuring, careless editors divide the sentence to equal parts and link each part to the articles. That way we'll get a mess that turns nearly the entire sentence blue like this:
The reader has no clue there are multiple links there. If they do discover all the links, it is a pain following all the links. Don't do this, please.
Covert opinions: Too many times sinkholes are used to bury a YMMV in an example or description. These are bad. If you see one of these, remove the unnecessary links and/or restructure the necessary ones.
Linking a common phrase to a trope of the same name: For example, linking a statement that someone "got better" in some way, shape or form to the trope I Got Better. That is part of why the trope was renamed to Unexplained Recovery and why No New Stock Phrases are allowed.
Changing the display text of a trope in a list: This is used to make a trope specific to a situation, e.g. changing Sealed Evil in a Can to Frozen Evil in a Lake. However, doing this messes up alphabetization (does that example go under S or F?), makes it harder to find tropes, causes confusion over what the trope's actual name is, and encourages Zero Context Examples and Square Peg, Round Trope. Just list the trope under its normal title and then expand on it properly.
Trope potholes in page quotes: Quotes do not have potholes in their original medium, and extraneous bluelinks above the trope description just distract the reader. If potholes are not necessary to understand the quote, then they are redundant. If potholes give context that is needed to understand the quote, then the quote does not truly illustrate the trope. Page quotes thus should not have any trope potholes in them, although it is okay to pothole to a work or genre which is referenced directly.
Joke Fulfillment Links: Please consider that for tropers or readers who have been frequenting the wiki for even a few days, there is nothing remotely original or new about potholing understatements to Understatement, stealth puns to Stealth Pun, running gags to Running Gag, overused running gags to Overused Running Gag, and so on. It has been done to death. It has become repetitive and predictable, and repetitiveness and predictability kill humour. In other words, don't require a link jump to make the joke work. It doesn't. Ever.
Hiding work names in the examples on trope pages: Potholing the actual name of a work to a character, location, or creator's name. This is both a misuse of potholes and a form of Fan Myopia. Always clearly state the source, preferably at the start of an entry.
Reaction potholes: Some moments in a work may elicit strong emotional reactions from you. Many of these reactions have tropes for when they happen in fiction. However, potholing to a trope that represents how you personally reacted to a scene, such as potholing to Oh, Crap! for a scary scene, or to Flat "What" for a confusing one, is not relevant to most readers and should be avoided.
Check out Weblinks Are Not Examples for more on how to avoid using links irresponsibly.