I've leased the last couple of vehicles (strictly personal, not business) because of cash flow implications, here's the data....
A typical lease is 3 or 4 years. In that time, you're paying for roughly 50% of the vehicle cost (so a 50% residual at the end of the term, this is rough, in reality it depends on the vehicle and such)
During that time, you're only paying tax on the 50%
If you buy the car and finance it, you're paying for the complete purchase price in a similar amount of time (4-5 years usually). So you've got twice the $$ to pay back in a similar amount of time plus the full tax.
So even though the interest rate is less on the financing option, the lease payments are far less.
When you lease, you can get different mileage allowances. The 3 common ones are 16K, 20K or 24K per year. If you go for just 16K per year, the payments will be less and the residual will be higher. However, as BBB points out, if you end up using the car more than this you really get penalized. I've gone for 20K per year and just manage to stay under that.
Lastly, at the end of the lease term, the car is quite often worth more than the residual. In this case, you can pay the residual (and the associated taxes) and either keep it or sell it privately to make a few bucks. Toyota/Lexus is one brand that usually ends up like this. If the vehicle isn't worth more than the residual, just give it back and move on...
If the cash flow doesn't bother you and you intend to keep the vehicle for a long time, financing is always cheaper versus lease....