The biggest advantage to using one of the major practice management softwares hands down is the integration it offers. I use Kodak's Softdent in my practice, and with that 1 program, it handles, my patient records (x-rays included), scheduling, billing (both e-claims submissions to insurance companies, self pay, and third party finance company payments), back records(billing statements, proceddures done, missed appontments), form letters for missed appointments, missed work/school excuses, referral letters, as well as entire practice indicator calculations just a mouse click away (production/collections over any interval for any or all billing providers from the 1st day I started using softdent, hourly productions by provider, etc, etc etc.
Could you get away with just something like excel, sure, but then you'd end up with another program for scheduling, a different one for e-calims submissions, etc. The major practice management programs just integrate all you need to run your practice into one program that very often includes real good tech support to boot!