I have used tapes several times in court---to impeach false testimony---you know, to help a LIAR's memory. Courts won't let you bring tapes in directly, but they CAN be brought in to refute false statements by the opposition.
I don't USUALLY tape conversations, but there have been several times when I thought someone was starting to act strangely in a business situation, and would tell me the truth directly, but was sending strangely different signals in their behaviour, so I secretly started taping our conversations.
Sure enough, in EVERY case, they developed amnesia when a really important time came for the truth to be stated. And in EVERY case, their sudden onset of amnesia disappeared---AFTER the tapes came out.
One warning before considering taping, of course, is that YOU must be telling the truth at ALL times, so that in the end, it is NOT "YOUR word against THEIR word," it is "THEIR word against THEIR word!" How can they argue with that? Answer: They CAN'T!
Oh, and if they say "I don't recall" as an answer, and YOU DO recall the situation vividly (and can TRUTHFULLY swear to it under oath), a lawyer of mine once asked the defendant "well, if YOU DON'T recall, and my client DOES RECALL---VIVIDLY---would you have any reason to doubt his/her recollection?"
The good news is that the defendant has two choices: (1) The defendant will virtually certainly say no meaning that YOUR recollection is taken as FACT (and it BETTER be true!!!!), and (2) If they say yes, they are ADMITTING they DO recall and have just PERJURED themselves in the previous claim of not recalling. Either way, it is a WIN-WIN for YOU---again, assuming YOU are telling the truth and the defendant is lying. It worked like a champ!