Not to waste the Tziburs time
with a Kapitel Tehillim
The Gaon's Minhag was not to say לדוד ה' אורי
from R. Chodesh Ellul till Simchas Torah.
The אדרת* writes the reason for not
saying it was because of טירחא דציבורא.
Saying one extra Kapitel Tehillim takes
up too much time of the Tzibbur.
Perhaps we can explain the Aderes /Gaon,
There is no mention in Bavli, Yerushalmi,
Rishonim, Tur, Shulchan Aruch, Kisvei Arizal etc.
to say לדוד ה' אורי (in Ellul)
The first to mention to say it בציבור** is
the Sefer Chemdas Hayomim*** & the Sefer
Shem Tov Katan which are Sifrei Kabbala****.
The Gaon, in general, was against adding
additional Tefillos & Pesukim. He tried to stick
to the original Tefillos of the Anshei
A Shliach Tzibbur who starts one minute
late in a Minyan of 100 people, wasted
not one minute but 100 minutes. (Tircha
of 100 people times 1 minute)
Adding a Kapitel Tehillim which takes
to say only one minute can at times
be considered taking 100 minutes.
This might explain why the Gaon
considered it טירחא דציבורא and
didn't add it to the Tefilos during Ellul etc.
א' אלול most Shuls will be
saying 3 Kapitlach Tehillim at end
1) שיר של יום
2) לדוד ה' אורי
3) ברכי נפשי
According to the Gaon, we don't say the regular שיר של יום since the Levi'im didn't say it on Rosh Chodesh & Yom Tov. All you would say is ברכי נפשי which was the שיר של יום of Rosh Chodesh.
*הרב אליהו דןד רבינוביץ תאומים
(he was a twin)
**The Sefer Shem Tov Katan
printed before the Chemdas Hayomim
mentions only to say it ביחיד .
***major controversy who the
author was.Some don't say
Ledovid Hashem Ori (Ellul)
claiming the source
is Nasan Ha'azasi yms.
**** I believe the first Halacha Sefer
to say it is the Mateh Efraim