absolutely ALWAYS backstitch!
the only exception to the rule is if you are topstitching a seam and the backstitching will show, in which case tying the thread ends off is perfect
you should also always backstitch at the start of the seam so that it doesn't start unravelling!
sorry if I seem waaaaayyy too obsessed about this, but I used to hand tie every single seam, which probably doubled sewing time on most projects
Then I got to university and met the lovely industrial sewing machine with built in backstitch function! It is my new best friend and automatically backstitches at both the start and end of seams (although, my tutor found out that I was using the 'auto' function and now comes over and turns it off! So I turn it back on, and it's now a running thing.. but I'm waiting for the day she actually gets mad at me for it!)
And that got rather long winded....
Good luck with your new machine!