No participating in D-day or Pickett's Charge, no attendance at the first Constitutional Congress, no Agincourt, no hanging with the Vandals at the gates of Rome, no sitting down with Eusebius at Nicea, no walking with Jesus through Galilee.
In short, no fun at all.
This idea has always seemed more plausible to me than actually travelling back in time. Of course, considering that we don't even have the technology to view the flag we planted on the moon, from telescopes on Earth, this is pretty far-fetched too. Not to mention cloud cover on Earth obscuring events in the past, and forget about anything important that happened at night.
It occurred to me that visiting the past will never happen on Earth, because if it were possible, we probably would have been visited by someone from the future by now. Maybe. Damn, this stuff gives me a headache!
All we have to do is find and stabilize a naturally occurring wormhole that exists in the deep past. Simple!
I don't know about Pickett's Charge. But it would have been interesting to provide about 25 hand grenades to A.P. Hill's corps trying to knock Joshua Chamberlain's 20th Maine off of the Little Round Top near Gettysburg. If the LRT had been taken by the Confederacy that day, the war might very well have been over and Lee would have been cooling his heels in Abe Lincoln's chair.
Or, take it back a few years - give WB Travis a couple of boxes of Claymore mines to place around the Alamo.