Here's what goes through my mind when trimming bushes and hedges:
Can I do what I need with manual shears and loppers? Easy, makes nice cuts, I can shape easily. I shy away from using them if I have LOTS of stuff to cut.
Are the branches all small (< 1/2")? If there are branches bigger, I'll still start with the hedge trimmer anyway, and when I hit the bigger branches, Ill jam the trimmer and curse a bit.
Then I'll look at the branches a bit closer. If I angle my trimmer a certain way, can I get that branch cut? Ok, if the branch is too big, then I bring out the manual lopper, reciprocating saw or chain saw. If it's a floppy, bouncy branch - it's probably not too thick, and better handled with loppers. I go with the reciprocating saw if I target a specific branch I want out, and it's steady not floppy and it's less than 2" or so. A longer 12"+ pruning blade can fit through other branches and do less damage to stuff you dont want to cut. A chainsaw, given it's large size, is just going to whack at anything in it's way. But it's great if you have clearance to get to a branch, and it cuts much faster. The reciprocating saw will bounce around on floppy branches making the branch shake and chainsaws given bigger weight make the branches and the saw bounce back and forth off each other.
You can probably significantly hurt yourself with any tool. I lent my chainsaw to a neighbor once, (responsible guy) who decided that the bounce back way not so good. so he decided to hold the chainsaw with one hand and to hold the branch steady with the other hand. After a visit to the ER (he sliced his hand open, fully recovered in a month), my neighbor's wife politely asked me never to loan her husband a power tool again.