The joke is not complete once you add the period. Jokes can evolve and transform into something completely different and unless you have a steel trap of a memory, you will forget that tag or improv piece that you added. When I started out I never really recorded my sets and now look at me, I’m a hobo living in one of Shaq’s discarded shoes because I wasn’t paying attention.
Recording your sets is great if you are one of those comedians that make a lot of things up on the spot. It may not all be gold, but what is will be worth capturing. It’s not like you need a lot of equipment anyway. If you have a smartphone you can record with that. If you want better sound, then get a mic and attach it to your smartphone (can be found very cheap on Amazon). If you want a separate device, check out zoom and get the H1. It is a tiny recorder that you can put on the stool on stage or on a nearby table and get good audio. I have an H6 which is complete overkill. Don’t get that unless you are going to be connecting a band to it or need it for video work.
What I usually do is set the recorder either near me on stage or on a table where others are not sitting. Why? Because if your friends are comedians they will more than likely mess with your recorder and you will get their spoken manifesto instead of your set. You have to learn to set it out every time as well. It is not really gonna work for you if you only set it out once a week. The idea is to get all of your sets.
What are you listening for? You can be as broad or as detailed as you want with this. You can just listen to see if people are actually laughing at the jokes you are telling. You can see if you actually are telling the joke you are intending to tell (nerves can do that). If you want to be more detailed you can listen to see if you are speeding through jokes. Is it because you were cramming or because you are nervous? Are you cursing more than you would like? Are you using crutch phrases like hmm and like? These are things that your memory will not be able to replicate, but the recording of you will, and then once spotted, can be corrected.
Now, just recording the set is half the battle. You have to listen to your sets as well. I usually listen to my set when I am in the car alone. That way I don’t have anyone trying to correct material that I am still in the planning phases of myself. I am hyper critical of my material so it is hard for me to sit there and listen to my voice and my jokes. If you are one of these people, you just have to realize that it is suppose to make you a better comedian.