Climbing through a window is harder than it looks. First there are the logistics of making the window accessible (see: ripping the screen). Getting the window open the rest of the way is a no-brainer, but even if you push the panel as far as it’ll go, it still doesn’t leave a very large opening (I guess they figured most people would be using the door instead). If you happen to find yourself in a situation that calls for “breaking and entering,” make sure you think it through before you go bashing in.
Through a freak series of events, I found myself required to enter via window last Saturday night (thankfully a first floor apartment). Unfortunately for me, I did not consider my entry beforehand- I went for the head-first approach instead of the safer, feet-first approach- and am now (literally) wearing the consequences. But either way, whether you enter head-first or feet-first (or butt-first or sideways or upside down), in the end, it’s just not a good idea.
You’re going to end up hurting yourself. Whether you face plant into the hardwood floor, cut yourself on the window’s edges or whack something- your arm, your leg, your face- upon entry, it’s just not a pretty picture.
You could get arrested. Especially if the cops show up and you either a) don’t have ID to prove you live there or b) you actually don’t live there.
You will have a lot of explaining to do if someone sees you. Ties in a bit with the last one, but less serious- say, if your neighbor (who knows you) sees you. They probably won’t call the cops but they might think twice the next time you invite them over for tea.
You now have a broken window. Whether it’s your window or the window of someone you know (or don’t know), someone now has to pay to have the window fixed. If it’s just the screen, it’s not as bad, but either way, what a pain in the ass.
All in all, if you can avoid it (call someone with a spare key, call a locksmith or stop trying to break into someone else’s house), do so. If you truly can’t, well, be prepared for some battle scars.