There is no normal especially when you talk about systems from manufacturers since they tend to come preloaded with a lot of crap.  I would say for most daily driver use cases 8GB of ram is plenty.  If you're a gamer or use the system for intensive activity like compiling code, rendering, or gaming then more will be better.  RAM is meant to be used so high percentages are not really a bad thing.  It can impact the performance if your RAM utilization gets about 92% and stays that high.  This will lead to context thrashing which is when the CPU has to constantly swap memory content since there is no more free RAM.
RAM is also pretty cheap and easy to add or replace in most cases.