The logistics of each formation have already been explained so I'll go into detail about when and why you'd use any of these 'funky' formations.
I'll use the 4-4 to stop the run but I also use it as a different look and one that I'll blitz out of but leave myself with an extra LB or DLineman to cover up any short dump offs if the QB avoids my blitz. In a standard formation you leave yourself susceptible to a dump off and if they get past a safety they won't be caught.
I think the 5-2 is overrated and the majority of the time against the run my LBs make the tackle and if I only have 2 of them out there it limits my ability to have a LB hit the gap created by a defensive lineman sucking up a lineman or fullback on a block. I use it a few times a game to give a different look and confuse the offense.
I like the 3-3-5 because you have 3 LB's and extra DBs and if your DBs can tackel it can be an effective formation against both the run and the pass and with the team I use, Cincinnati, my defensive lineman suck anyway so if I can get one out there I'll do it and bring in an extra LB or DB. Hope this helps, if not, it wasn't that long to read.