Q.
Re- question 4276 you stated that If one made an Eruv Tavshilin, the
purpose is to provide the permission to do a usually prohibited work
in Yom Tov for Shabbos when needed. It fulfills it’s purpose
whether one used it or not, so the bracha recited on it will not
normally be an unnecessary blessing, and he is not obligated to do
some Melacha (work) on Friday to avoid a Bracha L’vatala (an
unnecessary blessing for the Eruv).
So why did Maran Rosh
Yeshiva Zt’l insist that he needed to do melacha to avoid bracha
levatala as was reported?

A.
Moadim Uzmanim (7; 122) rules that even if one already did everything
needed for Shabbos before Yom Tov began, one should still do and Eruv
Tavshilin with a brocho.

However,
Igrois Moshe (O.H. 5: 20) indeed disagrees and rules that if one is
certain that he has done everything for Shabbos before Yom Tov, one
should not recite a brocho before placing the Eruv.

In
reality, most often people have to do something for on Yom Tov Erev
Shabbos, so unless one is totally certain that nothing is needed the
brocho should be said.

As
we wrote: “the brocho recited on it will not normally
be an unnecessary blessing.” even according the Igrois Moshe.

Horav
Shlomo Miller’s Shlit’a opinion is similar.

Horav
Aharon Miller Shlit’a added, that since one should wash before
Shabbos begins his face, hands
and feet, and that is done with hot water, there is normally a
melacha done, and the brocho should be recited

Rabbi A. Bartfeld as revised
by Horav Shlomo Miller, Horav Dovid Pam, Horav Aharon Miller and
Horav Chanoch Ehrentreu Shlit’a