There is one key advantage to straddling at a full table and that is to make people
think you are a much looser player than you really are. Here's how it works. Let's say you're a tight player. If everyone
knows you're a tight player then you'll never get good action on your made
hands because once you start betting people will know you have a made hand and will fold. However, if people see you straddling then they may
think you just like to gamble and will treat you looser than you really are. Obviously, it requires people being observant which does not happen much at micro stakes, but it can be beneficial when paying against good (not great) players. Great players will figure out that's what you're doing, so you need to use this against a sweet spot of player skill.
The second advantage to straddling is that it pisses people off and anytime you can lean someone towards tilting it's a good thing.
Now, that being said, there is a time when you want to straddle every chance you get and that is when there are only 3 or 4 players in the game. Remember, late position is very important. Well, when there are only 3 or 4 players you are always in late position when it's time for you to straddle. So, you're essentially putting pressure on people preflop, getting to act last preflop, then getting to act last or near last post flop.
And finally, if your casino allows it, there is a button straddle which is where you are the button and get to straddle while being the button, which means you get to act last after straddling preflop. I try not to abuse this because it's really a low-class move in my opinion, but at some
casinos it is an option.