I think they fixed these, but some things that used to be an issue with those:
• amortization schedules would count that period as a "month" if you do a 12 month amortization schedule
• Same with rev rec schedules, though presumably ARM fixed that
• Some of the canned reporting/metrics also got screwed up (can't remember the details of how) due to the Adjustment Period
Could just be ** old man yelling at cloud ** going on here, but I do know there were a whole host of issues caused by adjustment periods at one point, so it would be good to do it in a Sandbox and validate they're not an issue anymore.