I found that when I installed Ubuntu Gutsy i386 on my Toshiba A215 when Ubuntu Gutsy AMD64 was already installed, the AMD 64 version was no longer on the GRUB list. I installed the i386 as it appeared some things from i386 were not available for the AMD64, and I wanted to compare the two. Unless you have exact duplicate service, it makes sense to allow both installs at once.
I found that when I installed Ubuntu Gutsy i386 on my Toshiba A215 when Ubuntu Gutsy AMD64 was already installed, the AMD 64 version was no longer on the GRUB list. I installed the i386 as it appeared some things from i386 were not available for the AMD64, and I wanted to compare the two. Unless you have exact duplicate service, it makes sense to allow both installs at once.