A Few Reasons Why Traveling Through Time Would Suck Shit...

You continue to age

Say you go a couple years into the future and you end up staying there for three years, when you come back you'll be three years older thus missing three years of your life. So you can think to yourself, "was it worth it?"

The food of the past is bad for you.

Thanks to our present your stomach will only be used to the politically correct standardized foods of our time, if you were to go back a couple centuries, the foods won't be as clean and sanitary as the foods are now so your stomach will practically tear itself apart after you eat some food of the past.

Nobody in the past can understand you.

The fact that language is ever changing, only allows you to go back so far into the future or to not go back at all. No matter where you go, you'll have to speak both period and possibly even regional dialect to avoid coming off as a spy, a rival neighbor, a hillbilly or a crazy person who may or may not be possessed by the devil.

If you travel far enough you don't exist.

Since everything has been kept on record for centuries now, because you've traveled far enough you'll have no form of identification to actually get a job of any sort. So basically you'd be living like an alien.

You're entirely broke.

The money system that we have would not be sufficient if you went farther than two hundred years back. The money system keeps changing and if you want to go back in time you'd probably get arrested trying to exchange it.

Time travel is all random.

Say if you did actually have a time machine, you'd have to take into account that the Earth is constantly moving at a high speed and it spins at a high speed as well so you'd only be able to change the year not the direct date otherwise you'd warp into space or you'd warp imbedded into stone or concrete. Plus the time you warp into would probably have a prejudice against your hair color ,ethnicity, or something like that. The world constantly changes so there's no way to tell the future and even with a history book, it won't help you very well.