I think as a rule you're better to have only a minimum amount of slack in the check chains. Depending on the geometry of your setup, you may need more or less slack to ensure the implement will fully raise or lower without binding, but I don't see, in general, much use or benefit in having the implement free to move laterally.
Having said that, I run my post hole digger quite loose, because it seems to work better when it has the freedom to "float" a little bit. I keep a little bit of play in my concrete mixer, too, since sometimes it's nice to be able to sway it back and forth a few inches. I keep a little B6000 with a trailer hitch mover on the back, and it's sloppy loose: Just enough to keep the arms out of the tires. It's absolute child's play to hook onto a trailer, since the hitch can move up, down, left, right, and with a gentle press on the tire I can roll it forward or backward 1/8" at a time if I want. My sickle bar mower I use to cut around trees I usually run a little slack, so it can float if I hit an unseen root or accidentally get a bit too close to something otherwise.
I run my box blades snugg-ish (If that's even a word...); same for my plow and disks. I've got a terracing blade I keep snuggish, as well as the tillers and tool bar. My brush hog on the tight side; I don't like any play at all back there, since it is so long and builds up significant momentum with any slack. I don't have a 3pt backhoe, but I wouldn't let there be any slack in there if I had one, having seen them operate.
I guess it really depends on what you're trying to get out of the implement. What are you trying to work out?