In a thread I suggested to use sudo su - to become root temporarily. I was advised that sudo -i would be a better choice.

I'm very curious why that is the case. Threads that I've found omit the dash from the first command, so don't apply.

Code:
"var"               |"sudo su -"                                                    |"sudo -i"
--------------------+---------------------------------------------------------------+--------------------------------------------------------------------------
"SHELL"             |"/bin/bash"                                                    |"/bin/bash"
"TERM"              |"linux"                                                        |"linux"
"USER"              |"root"                                                         |"root"
"LS_COLORS"         |                                                               |
"MAIL"              |"/var/mail/root"                                               |"/var/mail/wim"
"PATH"              |"/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin" |"/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games"
"PWD"               |"/root"                                                        |"/root"
"LANG"              |"en_ZA.UTF-8"                                                  |"en_ZA.UTF-8"
"SPEECHD_PORT"      |6560                                                           |6560
"SHLVL"             |1                                                              |1
"HOME"              |"/root"                                                        |"/root"
"LOGNAME"           |"root"                                                         |"root"
"LESSOPEN"          |"| /usr/bin/lesspipe %s"                                       |"| /usr/bin/lesspipe %s"
"LESSCLOSE"         |"/usr/bin/lesspipe %s %s"                                      |"/usr/bin/lesspipe %s %s"
"_"                 |"/usr/bin/env"                                                 |"/usr/bin/env"
--------------------+---------------------------------------------------------------+--------------------------------------------------------------------------
"XDG_SESSION_COOKIE"|"a7a40db8cf4c937acb049b764d08c288-1312375570.325101-1940988668"|
"SUDO_USER"         |                                                               |"wim"
"SUDO_UID"          |                                                               |1000
"USERNAME"          |                                                               |"root"
"SUDO_GID"          |                                                               |1000
Highlighted in red are the differences in the environment (mail, path and the 5 lines at the end). Please explain to me why sudo -i is the better choice.