Stop action is typically something like OK or Enter.
For example, on some cable boxes, you can enter up to 4 digits for a channel number. If the box sees less than 4 digits, it will wait a period of time before actually changing the channel.
Consider that you wanted channel 857 but you did not prefix with '0'. Remote sends
Send IR - 8 Send IR - 5 Send IR - 7
After some time period, the box will select channel 857.
Now say you realized that immediately after you pressed channel icon for 857, that you actually wanted channel 973 and you press 2nd button before the box times out on previous input and changes to 857.
The remote would send.
Send IR - 8 Send IR - 5 Send IR - 7 Send IR - 9 Send IR - 7 Send IR - 3
The box throws away the 8 and the 5 leaving 7973 which is likely not a valid channel number and definitely not what you wanted.
By setting a 'stop' action of IR Code 'OK' you can force the channel change. Now, the remote would send.
Send IR - 8 Send IR - 5 Send IR - 7 Send IR - OK (Causes the box to change channel immediately) Send IR - 9 Send IR - 7 Send IR - 3 Send IR - OK (Causes the box to change channel immediately)