Is visitor visa absolutely necessary while PR application in process?

[Leon]

If you apply inland, you should send in one package your application, request for visit visa extension while you are in processing and request for change of status to open work permit to be given when you get first stage approval.  That way, immigration hangs it all together and you don't have to worry about missing any dates.  With inland, if you have a good application, no interview needed, you can expect first stage approval in about 6 months and PR maybe in a year, could take 18 months, sometimes takes only 10.  If they have questions and you need an interview, you will not get first stage approval and it can delay your application by a year or more.

For outland, there is no first stage approval but it's faster, takes a bit over a month to approve the sponsor and after that average 5 months in Buffalo before you have your PR.