MacOS – Sleep / hibernation logic on OS X

Yes and no.

Without knowing the model of MacBook and level of Mac OS X - you may have safe sleep enabled by default. Safe sleep writes the entire contents of RAM to the hard drive, so anything that is still hitting the hard drive for IO might slow things down until the OS has suspended all the active applications in preparation for this write. It is theoretically possible this suspending process could take more time - but in practice I have never seen reports that it is measurable.

Recovering from sleep is the same since that means that power was not removed and the RAM contents were maintained. I would guess that the number of apps running does affect greatly how long it takes for the mac to become responsive again. Every app will start processing events (keyboard, mouse, periodic checks to save) so there will be a burst of activity to "catch" up to the current time. Newer OS also use launchd to kick off processes that should have been started while the machine was asleep. For example, the daily clean up script runs daily at 3:15 AM - so if the mac was asleep at that time, waking it up at 10am means the 3:15 script gets started as part of the waking from sleep which might slow things down. Add in several other processes on a full mac - and you get the slowness you are observing.

The no would be if you don't have it asleep over a time when events are started by launchd and if your apps are efficient or don't need to "catch up" - it really depends on your mac and the specific programs running.

In the end - if you want a more responsive mac when waking it and quitting apps makes that happen - do it! Don't worry of other people have different experiences. The apps you quit are most likely still in virtual memory (which is saved during sleep) so launching them again will be faster than an initial launch which is the entire reason why sleep exists. (unless you have less than 1/4 total RAM listed as inactive RAM in Activity Monitor).

edit: See this as the behaviour has changed: Why won't closing the lid sleep my MacBook Pro with external monitor attached after upgrading to Lion?

There are two groups of people. Those who wish to have dual displays and have closing the lid go into sleep and people who wish to disable the monitor display, close the lid and use the external monitor as if you had 'docked' with it.

Previously, if you wished to switch from the macbook to an external monitor entirely then you had to perform the following to put the laptop into clamshell mode:

1. Make sure the computer is plugged in to an outlet using the AC power adapter.
2. Connect a USB keyboard and mouse to your computer.
3. With the computer turned on connect the Apple portable (using the appropriate Apple adapter if necessary) to the appropriate port on the external display or projector and turn the display or projector on.
4. Once your computer's Desktop appears on the external display, close the computer's lid.
5. Once the lid is closed, wake the computer up by either clicking your mouse button or by pressing a key on your external keyboard.

source: http://support.apple.com/kb/ht3131

So to put the machine in clamshell mode required you to put it to sleep and wake it back up again. As far as user experience goes, that is somewhat jarring.

As you have the other options to put the machine to sleep, it seems very likely that this change will remain.

Right now, there is no way to alter this behaviour.