That's exactly it. And it does make it much easier to multiboot!
A guy who comes around here once in a while, Saikee, has 100+ OS's booting from grub in this way.
The only downside I've seen so far is that generally whichever grub is in the MBR should have a separate /boot partition when you install that first linux. That's because in your case, if you ever want to get rid of Mepis, you'll delete the / partition for Mepis which has /boot/grub and all the config files for grub that is installed in the MBR. So then you've produced an unbootable hard drive.
If you have a separate /boot for Mepis, then grub still has it's config files even if you nuke Mepis. All you have to do from your new distro is modify the Mepis /boot/grub/menu.lst to chainload your new install.