1. Consecutive life sentence is merely a symbolic measure for the victims' family. It has no true legal effect.
Instead, the consecutive life sentence provides a relief to the victims' family that the convicted is responsible for each of his/her victims.
2. Life without parole, in plain language, means life imprisonment without chance to parole. Unless a pardon is granted (which is unlikely, even if granted, it will convert to life with parole only), the person stays in the prison forever.
However - it has more meaning that it looks. Life without parole is only offered as an option for first-degree murder as an alternative of death penalty when there is either not enough evidence to support death penalty or the state has banned death penalty.
All other life imprisonments are life with parole.
3. No. 100-year of imprisonment does not mean the person has to serve 100 years.
When certain conditions are met (good behavior, restitution, etc.), each state allows prisoners to petition for early release or parole.
And surprisingly - 100-year sentence is not a life sentence in theory, but in practice.
4. No - it actually simplifies the process and will result more conviction. By using this doctrine, a court need to analyze the suspects' behavior (does A lead to B?). However, without this doctrine, the court simply need to focus on the evidence support each of the charges.
For example, you broke into a car and stole some valuable. Under this doctrine, you will be punished for breaking, not stealing (as stealing carries less severity). However, with this doctrine, you will be punished by both.