There is a very substantive difference between the penalties that can be given to a chess player in time pressure depending on whether it is USCF rules or FIDE rules. As you can see Fide rule 8.4 states that if the increment is smaller than 30 seconds, then player is not obligated to meet the requirements of rule 8.1 which essentially mean player is required to keep score.
The corollary to this, of course, is that if the increment is 30 seconds or greater, one must keep score, move by move, whether they are in “time trouble” or not.
My understanding is that if you have lost track of your score in time pressure, then your opponent can insist that you catch up on your time which could lead to a possible time forfeiture if you are unable to to accomplish the task.
The FIDE Laws of Chess, Article 8.4 states “If a player has less than five minutes left on his clock at some stage in a period and does not have additional time of 30 seconds or more added with each move, then he is not obliged to meet the requirements of Article 8.1.”
|In the course of play each player is required to record his own moves and those of his opponent in the correct manner, move after move, as clearly and legibly as possible, in the algebraic notation (See Appendix C), on the scoresheet prescribed for the competition.|
|It is forbidden to write the moves in advance, unless the player is claiming a draw according to Article 9.2, or 9.3 or adjourning a game according to the Guidelines of Adjourned Games point 1.a.|
|A player may reply to his opponent’s move before recording it, if he so wishes. He must record his previous move before making another.|
|Both players must record the offer of a draw on the scoresheet. (See Appendix C.13)|
|If a player is unable to keep score, an assistant, who must be acceptable to the arbiter, may be provided by the player to write the moves. His clock shall be adjusted by the arbiter in an equitable way.|