"Will be doing" vs. "will do"

"I will eat cakes" is more about the act; "I will be eating cakes" is more about being in the state of "eating cakes". Consider "I will drive home tomorrow" (yay, I'm going home) versus "I will be driving home tomorrow" (so that would be a bad time for you to call me on my cell phone).

Both of these refer to the future, and both are correct and can be used in any situation. However, there is a slight difference between "will be" and "will".

The simple form is as it suggests referring simply to what happens next but the continuous indicates or suggests a picture of activity in the future.

For example,:

I will walk home.

and

I will be walking home.

Both refer to walking home in the future, but the first statement is used when referring to the next thing you are going to do i.e. during after school, while the second statement can be used anytime from the day before to just before going to school.

Also, there are instances when one or the other can not be used. For example,

I will be good.

but not

*I will good.

The second example is incorrect
Because "will" is only a modal verb, it needs another verb, otherwise the sentence is incomplete. There are instances when "will be" has to be used, and "will" can't be used.

The first form is used when it is relevant that the action will occur at the same time as some other action. For example:

Don't bother calling after 9; I'll be sleeping.

There's an old American children's song that might help to highlight the distinction: "She'll Be Coming 'Round the Mountain".

She'll be coming 'round the mountain when she comes, (when she comes).

She'll be coming 'round the mountain when she comes, (when she comes).

She'll be coming 'round the mountain, she'll be coming 'round the mountain,

She'll be coming 'round the mountain when she comes, (when she comes).

And the best part? We'll be havin' chicken and dumplings.