That's a tough question. It depends on a number of factors that only you and the person arrested can determine.
The cost associated with bail can be high and usually involves the services of a bail bond agent. Typically they'll charge a non-refundable 10% (or less) of the full amount of the bail and collateral for the balance (depending on the amount). There are many such agents available, but not all are equally straightforward in their business dealings, so I'd pick someone referred if at all possible.
If you have the funds to bail your loved one out, the next question is basically cost/benefit. If he/she has a good job and can't afford to lose it, it may be worthwhile bailing him/her out. But if the crime is very serious, or if he/she has a serious record, it's very possible that he/she may be facing substantial jail or even prison time. In that case, bailing someone out may simply be postponing the inevitable.
Sometimes it comes down to a choice of bailing someone out or hiring a private defense attorney. That decision comes down to how much faith one has in the public defender's office. Without being too critical of the public defender, I think it's fair to say that in most cases a private defense attorney will spend more individual time with your loved one and be much more accessible to answer questions and explain the process. Keep in mind that the "P.D." has a very large caseload and may not have the time to adequately prepare or pursue all viable alternatives.
In any event, if someone close to you has been arrested, in my experience it's important to have an private attorney come into the case at the beginning. In some instances that can make a big difference in the outcome of the case.