If you were thinking of a 10g, why not go a little larger? The additional cost and additional space requirements are negligible.
The hardest thing about a pico or nano is keeping up with evaporation. Depending on your indoor environment, forgetting to top off for a day or two can cause salinity to rise enough to kill things. So this means you need an ATO device & fresh water resevoir (auto top off) which can be hard to stuff in a small tank. A full glass top may retard evaporation but can block light & hinder oxygen exchange. If you try to top off by hand, you've got to have perfect performance 365.25 days per year.
Also, just adding a little more food one day can skunk a small tank really quickly. Temperature changes and a pump failure for example can happen and the bad consequences can happen fast, much faster than on a larger tank.
Small tanks of <10g can be done and sustained for a long time, but the system has to be very well thought out and employ the right equipment, and must be monitored carefully. Often, one mistake is all it takes to crash a small tank.