There is no difference in processes between sudo -i and sudo bash. Have you ever actually checked?
That said sudo bash does something a bit different than sudo -i
For one, doing a sudo bash does NOT clear out the calling users environment, sometimes you actually want this.
Another point is that sudo -i will always run with the login shell for the account, which may be set to /bin/sh which is often not bash, which may or may not be what you want.
So since you've never checked regarding process numbers with sudo -i vs sudo bash, here you go:
Here is with sudo bash, you'll note that the PS1 gets updated, but the current working directory doesn't get reset and most environment variables are preserved, which might be helpful if you'd like your PATH and DISPLAY variables to be preserved.
[androsyn@random-host ~]$ sudo bash
root@random-host:/home/androsyn# ps T
PID TTY STAT TIME COMMAND
7558 pts/11 Ss 0:00 bash
7870 pts/11 S 0:00 sudo bash
7876 pts/11 S 0:00 bash
7877 pts/11 R+ 0:00 ps T
root@random-host:/home/androsyn#
And sudo -i you'll note that you are fully cleaned root login, the equivalent of "sudo su -"
[androsyn@random-host ~]$ sudo -i
root@random-host:~# ps T
PID TTY STAT TIME COMMAND
7690 pts/10 Ss 0:00 -bash
7903 pts/10 S 0:00 sudo -i
7909 pts/10 S 0:00 -bash
7912 pts/10 R+ 0:00 ps T
root@random-host:~#
Now what I suspect you are referring to is the extra process required for running "sudo su -" and you would be correct about that.
[androsyn@random-host ~]$ sudo su -
root@random-host:~# ps T
PID TTY STAT TIME COMMAND
7690 pts/10 Ss 0:00 -bash
7962 pts/10 S 0:00 sudo su -
7968 pts/10 S 0:00 su -
7975 pts/10 S 0:00 -bash
7978 pts/10 R+ 0:00 ps T
Not that the one extra process is going to bring down the system...