For Rogues, the benefit of STR is two-fold:
1) It raises your attack power, which as a result, raises your damage per hit, not above the cap, but the average goes closer thereto.
2) It raises your damage per backstab ever so slightly per point. Raise your STR enough, and you'll see a significant raise in BS damage.
Raising STR, Dark Elfs have an advantage over short races since they can use
Hero Bracers, but the best race for rogues is normally Barbarian because they can use
Tree Weave, too, and then use the
MoD to turn into a Dark Elf.
For starting stats, always fall back on
HBB's post.
STA or GTFO.