Question Regarding Aftermarket Launchers

[RajCaj]

I'm using the Google Now launcher on my Galaxy S4, but noticed that it seems to lag at times.

My question is, does the default launcher (TouchWiz) continue to run in the background, when running an aftermarket launcher?

If so, could I improve the performance of my aftermarket launcher by lightening the memory load on the default launcher (remove all widgets & other things that use RAM)?

Thanks in advance!