You could argue both ways, although you'd have to stretch a little more to accentuate the positives of the purges. But I'll try on both.

For the negatives:

• The purges had disastrous effects on cohesion because networks were eliminated, not individuals. We kill this general, and everyone who ever worked with that general or had dinner with him at some point or lived in the same village or apartment block. So for the innovators that were arrested and killed, their innovations died with them.
• Personal relationships with Stalin or political reliability were more important that martial skill to maintain your position in the military hierarchy. Stalin was surrounded by "yes men" and sycophants who wouldn't want to deliver bad news until there was no way to hide it. Stalin wasn't told about setbacks, they waited until the massacres couldn't be hidden or Stalin demanded units advance which no longer existed. Mikhail Tukhachevsky, who helped develop the tactics that became blitzkrieg between the wars in a joint project with the Germans, had been killed in the purges while his German counterparts (including Guderian and Model) were in high-up positions at the beginning of the war.
• A lot of those who were eliminated, whatever their supposed crimes, were eliminated for being good at their jobs. Kulaks, for example, were relatively prosperous farmers. Some got prosperous by manipulating or cheating their neighbors, sure. But a lot got prosperous because they were good at fixing tractors and taking care of horses, knew when to plant and how deep, saved their excess and spent it to improve their farms. A lot of inventors were eliminated had developed something that challenged doctrine (and the champions of doctrine were typically highly placed and closer to Stalin's ear).
• It was an era that prodded people into either inertia or hysteria. You can keep your mouth closed and eyes down and just try to get through this shift, this week, this year, without pissing someone off. Or if you have a temporary setback, know who to blame. Why were you less productive today? Someone must have sabotaged my lathe, comrade! This institutionalized lack of initiative showed up a lot during the early stages of the war.

For the positives:

• It bred the "us versus them" narrative and really worked it into the bone and sinew of the average Soviet citizen. We are all against the Kulaks and the Trotskyites and so on. Now we are all against the Nazi oppressors. There was a hierarchy and process in place to systematize a reaction against a particular group, so they essentially just needed to do a "find and replace" in the proverbial Microsoft Word file and slip "Nazi" in there in place of whoever it was we hated before.
• It became instinctual to notice the eccentricities of outsiders. The purges were a "nail that sticks out gets hammered down" time, so anything out of the ordinary was reported and punished. German efforts to develop native intelligence during the war would be coming up against this, so any agents recruited by the Germans would be, theoretically, more easily sniffed out.
• Some of the gulags became de-facto "think tanks." When all the intellectuals in a field are arrested and deported at the same time, a lot of them end up in the same camps and can actually improve their expertise due to exposure to colleagues they would have been separated from in civilian life. In addition, those that weren't arrested abandoned all political notions and volunteered to basically be slaves to the state, saying essentially "we'll shut up, just give us a problem to solve and we'll solve it." A whole system, called sharashka, centered around that - get a bunch of experts together, isolate them, and give them a problem to solve. Maybe not the same material scope of the Manhattan Project but certainly the same idea, multiplied to cover a bunch of different subjects concurrently.
• Many of the great projects and much of the raw material extraction and weapons production of the time were built by gulag convicts that had been rounded up in these purges. Highways and factories had been built by convicts. Cobalt, tin, nickel, and gold were primarily extracted by convicts. A lot of the tanks and airplanes were built by convicts.
• It was an existing infrastructure to throw prisoners-of-war into once they encountered them.