Keeping your phone in only LTE/4G will drain your battery less and the connection will be more steady.
5G provides higher throughput (speed/bandwidth), but only if you're close enough to towers without obstructions with materials which block the different frequency signal. Over time, it degrades your battery quicker, because you need to charge it more often.
You don't need all that speed on the phone. Like ever, unless you need to update your OS and it's gigabytes of data.