My granddad used a brush and double sided razor. My dad uses heated foam but no brush.  I see a lot of you guys use a brush to apply the foam. Why? What does it do that just applying by hand doesn't do?

Thanks for helping me understand.

like sialor61 said it helps lift the whisker up an I think helps mousterise the skin too

I actually use cheap hair conditioner to shave my head with. I wonder if you could use a brush with that?

yes - it works great with 'slick or any other cream product.  it's much more effective than just your hand - plus after you master loading up the brush it allows you to keep a ready supply of lather for a second pass or touching up a spot you may miss.  Most likely all you'll find in stock at local retailers are the cheap boar bristle brushes - if you go that route see if you can get a small stand so it can be stored/dried with the bristles down.  Boar tends to spread/distort a bit more than badger.  As a dedicated bowl and brush guy I suggest Amazon for an entry level badger brush and a Marvey hard rubber cup. (it's the dark one and being rubber is vwery forgiving of being dropped etc)  the mug should be around 10 bucks.  And if you;re into menthol aftershaves for the summer I suggest Osage Rub - my facwe/head is about numb from the "cold" after I use it.