Use of ISpell dictionaries with tsearch2 - what is the point?

I'm new to using tsearch2 and am trying to understand why I would want to
use an ISpell dictionary before the stemming dictionary. I'd originally
hoped that ISpell would suggest corrections for misspelled words as the
documents that I will be indexing will contain a lot of spelling mistakes.
>From what I now understand ISpell dictionaries only recognize properly
spelled words. This means that any misspelled word will be handled by the
stemming dictionary and usually just passed as is.

1. If I am correct about this then what is the point of using the ISpell
dictionary in the first place?

2. Is there a solution for correcting spelling mistakes in the documents you
index? I have seen the readme files for pg_trgm,
http://www.sai.msu.su/~megera/postgres/gist/, which would allow me to
suggest other terms for a query if the misspellings were common enough. I'd
rather fix the problem at index time so that querying with the proper term
would find any misspelled terms (within reason).