There are numerous issues. First, let's make sure you understand that the collection of protected data must be preceded by a warrant, not the other way around. For instance, you don't, as a law enforcement officer, get to search every house a subdivision without a warrant and then, once you find something illegal, go before a judge and get a warrant for the houses that had illegal items in them. To declare otherwise is exactly the opposite of the due process of law.
That being said, and to speak directly to your example of recorded "but not used in any way without a warrant" I have two words.
Or, phrased another way: You will never know if, when, and how illegally obtained information is used against you by law enforcement. They will make up a good reason, a plausible reason, a well thought out, even impeccable reason why they have the information about you that they do. It will be completely false. It will be designed with the intention of deceiving not only you and your attorney, but also the court, the judge, the jury, and possibly even the prosecuting attorney as well. And not just them, as we know cases are recorded. Precedent could be set for all time based on illegal and deceitful actions on the part of law enforcement.
Not only would you never know that it was or was not used, but now you have an obvious 6th Amendment issue, subsequent to a violation of the 4th Amendment. To whit, they illegally searched you without your knowledge or the proper legal authority of a warrant, took the information they gained illegally and designed a plausible but completely false narrative as to why they would have that information, prosecuted you based on a lie, and prevented you from ever knowing your "accuser" at all by their deception.
You don't see a problem with this? This is not egregious? Well, keep looking. The details are pretty atrocious for other things that were done in secret. Something will eventually strike through that jaded and callous exterior you have. I am more sensitive to the protections afforded by the Constitution and view slights toward it personally, as they affect me personally.