Help understanding locale

I need some help understanding locales and what the impact upon my
database/application would be.

I am currently running 7.3.4 and have a database with tons of varchar
fields. However, when we query on one of the fields with a like, it
does not use an index. Apparently from the documentation, this is due
to the locale not being set to C. The locale command gives me the
following on my server:
LANG=en_US
LC_CTYPE="en_US"
LC_NUMERIC="en_US"
LC_TIME="en_US"
LC_COLLATE="en_US"
LC_MONETARY="en_US"
LC_MESSAGES="en_US"
LC_PAPER="en_US"
LC_NAME="en_US"
LC_ADDRESS="en_US"
LC_TELEPHONE="en_US"
LC_MEASUREMENT="en_US"
LC_IDENTIFICATION="en_US"
LC_ALL=

I am just starting a project to do an upgrade to our application and
looking at trying to fix this problem since it is affecting our
performance. I have upgraded our dbserver to 7.3.7 (our next project is
a major db upgrade to 7.4 or even 8), and created a new cluster with the
locale specifically set to C (initdb --locale=C ...). This has fixed
the index usage problem, but I don't understand what ramifications if
any it has on my database. Please help me understand what this means to
me as the dba.

Thanks,

Chris