In a game I DM'd, a PC had cast a spell with a Concentration requirement and was subsequently Paralyzed. I quickly checked the description of the Paralyzed condition, which said nothing about Concentration but did say that the character was Incapacitated. I checked Incapacitated, which also says nothing about Concentration. I thus ruled in-game that the PC could maintain concentration on the spell even while Paralyzed.
However, post-game, I read the description of Concentration, where it clearly says that you lose Concentration when you are Incapacitated. It seems (in my opinion) like that is an important enough consequence of the Incapacitated condition that it should be listed with the description of the condition.
What the question is:
are there other mechanical consequences of Incapacitated that are not listed in the description of the Condition itself, but are found somewhere else?
What the question is not:
One of the Consequences of Incapacitated is that a character cannot take actions or reactions. Abilities that require the use of actions or reactions are therefore already assumed to be prohibited and do not need to be listed as part of an answer. Maintaining Concentration does not normally require spending an action or reaction.
What the question is also not:
I am principally interested in consequences that I should track as a DM and that, as with Concentration, would not be immediately obvious. I would consider class-, feat-, and race-based abilities primary the responsibility of the player. For example, the player of a Barbarian who wants to use Danger Sense should know how Danger Sense works, but as a DM, I will have numerous NPC's with Concentration effects so that is something I should know. Likewise, a monster with a special effect ended by Incapacitation would not need that listed here if it was included in its stat block, but if the stat block just referenced a general ability that would then need to be looked up as well, that would be a good candidate for the list.
Best Answer
This answer only lists the otherwise unlisted effects of each condition that could apply to practically any character (that I could find, of course).
It does not include class-specific examples, race-specific examples, feat-specific examples or other such things. Similarly it does not include monster-specific examples. An example of something not included here is that a Barbarian cannot benefit from Danger Sense while Incapacitated.
Some of the things below are also extreme technicalities; I opted to include everything I found instead of trying to make some sort of cutoff for inclusion.
Grappled
Incapacitated
An incapacitated creatures does not count towards flanking (an optional rule from page 251 of the Dungeon Master's Guide).
An incapacitated creature does not cause disadvantage on ranged attacks in close combat.
An incapacitated creature can automatically be grappled and automatically be shoved.
An incapacitated creature loses concentration on spells.
An incapacitated creature cannot take actions which also prevents them from taking bonus actions.
Invisible
Prone
The prone condition does not describe what crawling actually means.
A flying creature that is knocked prone falls unless it can hover or is flying by magic.
A mounted creature that is knocked prone, must make a saving throw.
If your mount is knocked prone, you can use your reaction to land on your feet.
Unconscious