For what ever reason Samsung programs this "bit" of lag into the system and it can easily be removed by simply going into "Developer settings" and resetting the "window animation scale", "Transition Scale" and "Animator duration scale" to either 0.5 or if you still feel too slowed down you can set them to "OFF"! This is the same so called issue we had with the S4 and it works the same with the S5!
Absolutely no lag between apps!
Now for those having issue with the home screen launching you may want to go to "S-Voice" settings and make sure the "open via the home key" box is NOT checked! Again the same issue we had with the S4...the home screen is waiting that extra split second to see if your going to double press the home button...better yet go into App manager and just turn off S-Voice!
Now if your STILL not happy, download Nova Launcher and in "Nova Settings" under "Look and Feel" set the "Scroll Speed" and "Animation Speed" to "Faster then light"...If this doesn't make you happy, GIVE UP nothing will ever make you happy and you are destine to be sad and depressed the rest of your natural life!!! LOL! You may actually find that this setting is a bit too much as scrolling can get a little out of hand and toning it down a bit is better, it's up to you!
Seriously, I do not know why Samsung does this and it is a bit frustrating to have to go through this with every new device, I can only speculate they feel it makes the device more stable with a wider variety of third party apps, again, I don't know!
Cheers