I haven't played in games that have straddles, but in theory
their major purpose is to encourage action. The idea is that if one person straddles, then everyone else should be straddling as well. So you're disadvantaged for the one hand where you're UTG and putting in two big blinds without seeing your cards, but there'll be more money in the pot a few hands later when you're on the button or in the cutoff.
So straddles put more money in the pot, and they give poor players more opportunities to make mistakes too.
With insurance bets, again, haven't played using them personally, but the important thing to remember is they're (almost) always offered skewed in the favour of the person offering
The classic example was Phil Hellmuth taking insurance from Phil Ivey at the World Series last year (can't remember the event, but it was on ESPN). Every time Hellmuth got all-in against someone, he'd take out insurance from Ivey. Ivey very carefully set the odds
in his favour, and Hellmuth ended up owing him $20K more in insurance payments than he won in the tournament.
Side bets you've really got to just assess as they come up, as they can be on all sorts of things.