Technically you just have to rip the DVD main movie. However, I don't wish to ever split it to two dvd-r. So I rip ALL files so in case it I am not able to get it under 4.37GB then I'll do it with Instant Copy which requires all files (don't wish to re-rip all over again).
Now an easy way would but just to check the dvd while the dvd is in the dvd-rom prior to ripping. Sadly this doesn't work and results in erraneous file size calculations. However, when doing it from the ripped VIDEO_TS folder on the hd it's right on the money.
dvd2one also only requires ripping the main movie only. But I'm willing to wager that most of them still do CTRL-A for all files which I think just keeps your options open if this or that doesn't work out so we don't have to throw the original DVD back in to rip it at a later time.