You can and 'should' use it. It would minimize the number of classes in a stylesheet. Remember that it is cascading. The second class you will use, will add to the first one. Or at least it should according to the specs. That also means, that if there are conflicting settings, the second one would be the one used.
Example:
.initial {text-indent: 0; font-weight: bold;}
.second {font-weight: normal;}
If you now would assign it to a tag, e.g.<p class="initial second">, the text would not have an indent and normal font-weight. Of course this is just an example...
I do recommend always to check the result, since the cascading factor can sometimes surprise you.