Here we go again !
So Apple will be releasing their new operating system in mid to late September… It is my recommendation NOT TO UPDATE ! Please wait till we are close to 10.15.3 or beyond… currently in Mojave and High Sierra we are at 10.13.6 and 10.14.6
First rule… if it is not broken, do not fix it.
Also if you have a machine older than 2015-2016, even though machines from 2012 will be supported, I would not even consider upgrading. Your machine will run much worse than it does now, and after, you will want to consider buying a new one because you think it is the machine… it is not, it is the operating system not working well with older hardware.
If you do install and after change your mind, you can not go back… it will require a complete erase… so do not do it in the first place…
There are many article and thousands of people talking about this online and in various forums. Below are two links if your interested in reading more…
Oh, and by the way… do your back up today !