It is always a good idea to get a watch serviced if you plan to use it. The service interval for mechanical watches is 4-6 years. If they have not been serviced in many years (common) they can and will damage themselves by running. The NAWCC has watchmakers listed by area on the website.
The analogy I use is that of a car. You can drive a car until it stops running, doing nothing in the way of maintenance. A watch is the same, it will run until it is too damaged to run any more, or too gummed up or dirty to move.
Even NOS watches or watches that appear to be clean are dried out and filled with the residue of dried oil. My experience is that the 20's & 30's watches, especially the wristwatches, are usually very worn out. A watchmaker will be able to tell you if a favourable result is likely.
In reply to It is always a good idea to by Reverend Rob