So what sample rate should you be working out? There are different ways to look at this. There's not one rule, so let me run through all the different scenarios that I can think of where you can change the sample rate, and give you a bit of advice on that.
If you're just recording vocals in and processing, then I would say keep the session at 96, because then the whole process can be done at that higher resolution.
If you're a mix engineer, and you've been given tracks at 48, but you know it's going to go to 44.1 at the end, what I recommend is that you keep it at 48 for the session. You want to keep the session at whatever it comes in at when it was recorded. I wouldn't start doing loads of sample rate conversion at that point because the best way to do them is at the end after mastering, when you're about to put it out to all the different distribution channels. Then I would take the upper sample rate and upsample things to that.
I'm more inclined to upsample than downsample. Now what some mastering and mix engineers do is they'll upsample to 96 because certain plugins work better there. At that point, you'd be better off going in at that rate because it's going to make the plugin sound better and be a lot more high-def.
When you're a mastering engineer, you've got tracks coming in at all different sample rates for a session. What I do is if I get one track that's 96, one that's 48, and one that's 44.1, I upsample to 96 and do the whole session there. This means I can go out of my converters through the equipment at high resolution, and then capture again at 96 afterwards. Most of the time I keep it 96 because I'm a hybrid engineer, and I like to use EQs and limiters and stuff in the box after it's come out of my analogue chain. Then, I present that track to Spotify and all these different places.
Typically, I will downsample from 96 to 44.1 because most people want that format. The only people that want 48 are those working in production, music, or TV. Otherwise, when I'm dealing with record companies and the general public that upload to Spotify, I do it at 44K.