Does the client have employees? If so, they will also have to contribute at the corresponding contribution rate for employees that qualify - at least 21yo, worked at least three of the five years for the business and received at least $600 in 2020.
If the return changes and it affects that qualification while you are working, it avoids over-contribution and avoids excess tax. Or, you hardcode how much they want to contribute.
"is there any reason not to maximize?"
When the client can't afford it.
"Level Up" is a gaming function, not a real life function.