Purpose of Senate rule XXVI 5 (a)

[RadicalPi]

Here is the Senate rule that stopped the committee meetings:

XXVI. 5. (a). Notwithstanding any other provision of the rules, when the Senate is in session, no committee of the Senate or any subcommittee thereof may meet, without special leave, after the conclusion of the first two hours after the meeting of the Senate commenced and in no case after two o’clock postmeridian unless consent therefor has been obtained from the majority leader and the minority leader (or in the event of the absence of either of such leaders, from his designee). The prohibition contained in the preceding sentence shall not apply to the Committee on Appropriations or the Committee on the Budget. The majority leader or his designee shall announce to the Senate whenever consent has been given under this subparagraph and shall state the time and place of such meeting. The right to make such announcement of consent shall have the same priority as the filing of a cloture motion.

What was the original purpose of this rule? Why would the Senate want to stop its business so early in the day? I don’t get how this rule ever got started.