IANACL, but I’m trying to read up more on the various discussions. I can understand how a preemptive pardon might be proper for a group of individuals in some cases, but never for an individual and never for the president or potential criminal associates. The DOJ should have been allowed to decide whether to prosecute Nixon for obstruction. It’s possible they would have declined or offered a generous plea bargain with no prison time or fine considering he was already out of office.
At least a guilty plea would create a record. Since a pardon does not expunge a record, a post-conviction pardon leaves the offense on the public record, whereas a preemptive pardon deprives the public of knowing whether an offense was actually performed or not.