Two schools of thought on this IMHO;
1. Stain only exterior...
2. Stain inside & out...
I have always practiced "Staining inside & out" ( 2 to 3 coats outside (depending on the finish I'm getting,,, and 1 coat on the inside where the wood is seldom or never seen... I have never had any problems... Just my personal opinion...
Just because our ancestors only stained "exterior" that we know of, doesn't mean today's builder can't stain areas that will never, or seldom be seen...
So, again IMHO, it's up to you.
added note;
I want to mention one other thing as I didn't above , but I'll go back and edit my previous post;
I do use "Tru-Oil" after the final exterior staining, but never on the interior area's...