The thing to be aware of is if your blood or breath test comes back as a .10% or higher your chance of getting the charges reduced is slim to none regardless of whether you have an attorney. If by chance you get a DUI and see that the complaint says it is charged as a first-time DUI and you know you have a “prior” that qualifies, TAKE THE DEAL! The longer your case stays around, the more likely the District Attorney will realize her mistake and amend/change the complaint to add the prior.
If you are being charged with other crimes in addition to the DUI, such as a hit and run or resisting arrest, you will most likely want to hire attorney. These charges complicate things and increase the maximum and minimum possible penalty and an attorney is better equipped to negotiate deals in these cases including potential dismissals of certain charges.
Finally, if you think the officer didn’t have any valid reason to pull you over, you may also want an attorney. If there is no mention of any vehicle code violation, however, before the officer pulled you over, this means you have a valid “suppression motion” and need to hire an attorney to file and argue it on your behalf.