With the newly rejuvenated Deus Ex series still very much in the spotlight, some names within the community like Yahtzee have turned to the original to take a look at the roots of the series. Among the things that were mentioned was the fact that the original Deus Ex was a very free-roaming title. You could pile up garbage in people's offices, go places in buildings just to see if there were any particularly interesting bits of dialogue or Easter eggs associated with doing so, and you could do things like break the game by using the somewhat wonky physics engine to get places where you should be able to get or otherwise make the NPCs do really stupid crap. The point is that with the rise of more graphically intensive games, there was been somewhat of a lack in the area of "screwing around" space in titles, and while this may not seem important to most game developers and designers, a lot of gamers, myself included, believe that it's something that is sorely missed these days.
Now, I'm not saying that games should be spat out without beta testing or anything, dear lord no. That's just asking for the most horrifically nightmarish shitshow to grace any platform, something like another Big Rigs: Over the Road Racing or Superman 64. We don't need those titles. No, what I'm saying is that these days the developer response to thinking about what gamers will or won't do seems to have the almost knee-jerk reaction of "well, just limit them" without any real rationale as to why. Stuff like invisible walls, doors that might as be wallpaper, objects that have no purpose other than just just sort of being there since they can't be interacted with, and so on. Perhaps it is the price we pay for having more pretty looking games, but I think it's still a pretty high one.
Even though some railroading is often the case though, in a lot of these games players still try to find ways to just screw around. It's what made the sandbox genre so popular in the first place. If in Grand Theft Auto 3 you said "You know what, fuck the missions" and just decided to drive around, seeing what you could find or do, then you could absolutely do that. You could use cheats to spawn a dozen tanks, parade around while cops chased you, hell, you could even be a good Samaritan if you really felt like it and do the ambulance or firefighter side missions, or you could even be mundane and follow all the laws, not run anyone over or do anything out of the ordinary at all. I'll grant you that most people didn't just drive around being good little boys and girls, but the point is that if you wanted to, you totally could, and then if you got sick of that you could go throw a Molotov cocktail into a crowd or run people over or even, you know, actually do one of the missions that the game gives you.
Developers surely can't account for everything that a player is going to attempt to do. Hell, we've all done some strange stuff in games. I remember playing Goldeneye and just shooting the walls to see how many bullet holes I could get in there before the old ones started disappearing, and laying on proximity mines one on top of the other until there was a ridiculous stack, just to see how big the explosion would get and how ridiculous this gravity defying tower of discs that's jutting out of the wall could become. I hear stories all the time about people who kept holding up when Mario reached the end of a vine in Super Mario Brothers, just because they though the silly little animation he did as he tried to keep climbing to nowhere was funny, and people who played Fallout in the strangest ways just to see how much crap they could actually get away with (Protip: it was quite a bit, actually). Hell, even the origins of the combo started off as a glitch in one of the Street Fighter games, something that the dev team was confident that no one would actually find, let alone exploit; but players found it, and exploited it, and learned to counter it, and so on, and in the next Street Fighter, combos were feature, not a bug.
Screwing around and just seeing how badly you can break something, or if it can even break at all, is hardly a waste of time. In some cases, doing just that is what causes games to evolve and become better down the line, and even if that's not the case, it's not like the people doing this are wasting anyone's time but their own, although when you look at some of the results, and the popularity of programs like Garry's Mod which are almost built specifically to cater to such impulses, I can't really see where the time is being wasted, and neither can a lot of other people.