The updates are for fixing known problems and to give users more options/features.
The ultimate goal of the updates is to make things work better.
Some people have had problems updating.
I don't use Humminbird PC, but I have updated my 1197 five times without any problems (so far), and I am getting ready for the 6th update.
My reasoning for doing the updates is if HB has gone through the trouble of putting up a new update, it must be pretty important.
It may even make the system more accurate.
If you search on the HB site, it will tell you what a particular update affects.
The only problem with the updates is that you are supposed to set everything to factory defaults, do the update, then set everything to factory defaults again. If you ever went through the menus and set custom settings for yourself, you will have to go through the menus again and do it all over again (and for every update afterwards). But, I figure it's a necessary evil if I want to have the newest software for my machine. And the good news is that the updates are absolutely free.
Good Luck.