Every jurisdiction differs. Bear in mind that everything I say in this post pertains to my jurisdiction only. In mine there is no prohibition against suing for $170, but there are court fees and costs limitations in place to strongly discourage such a misuse of resources.
For example, if I run a regular case (as opposed to a small claims case), there will be court fees, but there will also be the probability of the loser having to pay some portion of the winner’s legal fees, with the portion based on how the case was run. What it really comes down to, is that through the awarding of costs, the system comes down hard on those who waste its time.
If my action is for less than $10K, then the regular court will refuse to hear it, and instead its small claims division will hear it. Again there are court fees, and again there are cost sanctions. Minimally, the fees will include $50 to start it up, $100 to set down for trial, and $35 for a writ of seizure and sale. Assuming there will be no motions (fees for those), examination in aid of execution (fee for that), or any other such detour (they all have fees), there will still be non-court fees for the sheriff, the process server, the title searcher, and the corporate searcher. That makes the case a financial loser from the git go.
To further discourage the waste of public resources on trivial matters, the small claims court puts a strict limit on how much it will award in costs to the winner. There is a schedule, but it comes out to only a few hundred for most cases. In small claims you can’t expect to be compensated beyond this amount for your legal expenses even if they run into the thousands. Note how this differs from the regular non-small claims court where there is no such cap. And here’s the kicker. If you are suing for less than $500, you are not allowed any costs award for legal fees or for your inconvenience and expense. Thus although there is no prohibition against actions for $170, the system ensures that the court fees will make it prohibitive, and that there will be no way to recover legal costs from the loser as there otherwise normally would be.
All this is still not enough to steer away hobbyists who have time on their hands and a few coins to throw away, so the system has set the initial filing fee for frequent users almost three times higher, and the setting down for trial fee about thirty percent higher. This puts actions for $170 into the realm of silliness.
I can’t speak for any other jurisdiction (especially concerning costs awards), but as you can see from the above, in my jurisdiction the system strongly discourages trivial actions, but does not prohibit them.
Fortunately, the disincentives are enough to ward off most hobbyists, so the system is able to tolerate those few who have a bee in their bonnet and don’t care about it costing significantly more to win than their potential winnings, and don’t care about their own social responsibility to not waste the public’s resources. If a significant portion of small claims claimants were hobbyists, then the system would simply re-adjust the fees and costs schedules accordingly to extend the disincentives already in place against trivial actions.