cross polination vs self polination - difference in breeding population? (Apr/16/2007 )

hi ,
was wondering why breeder usually grow larger population of cross polinator plants (eg potatoes) than
self -pollinator plants (eg barley)?

I was thinking that its because it takes more effort and labour to pollinate barley than potatoes whr u can jus leave it
to cross pollinate in the field.

Any other possibilities u could think of?

thanks

since potatoes are not self-pollinator plants, they need to me at higher population so the chance of cross pollination carried out by insects, wind , etc..becomes bigger